link to STAC API Extensions site instead of listing them (#381)

* link to STAC API Extensions site instead of listing them

* Apply suggestions from code review

---------

Co-authored-by: Matthias Mohr <[email protected]>

Author: philvarner

README.md

@@ -116,10 +116,9 @@ The *[item-search](item-search)* folder contains the Item Search specification,
 cross-collection search of STAC Item objects at a `search` endpoint, as well as a number of extensions. 
 
 **Extensions:**
-The *[extensions](extensions.md) document* describes how STAC incubates new functionality, and it links to the existing 
-extensions that can be added to enrich the functionality of a STAC API. Each has an OpenAPI yaml, but some of the yaml
-documents live as fragments in the [fragments/](fragments/) folder. The official list of STAC API Extensions
-is maintained [here](https://stac-api-extensions.github.io).
+The *[extensions](extensions.md) document* describes how STAC adds new functionality
+through extensions. The official list of STAC API Extensions
+is maintained at [stac-api-extensions.github.io](https://stac-api-extensions.github.io).
 
 **Fragments:**
 The *[fragments/](fragments/)* folder contains re-usable building blocks to be used in a STAC API, including common OpenAPI 

core/README.md

@@ -231,7 +231,7 @@ different conformance classes and a different set of links.
 
 ## Extensions
 
-None.
+STAC API Extensions can be found at [stac-api-extensions.github.io](https://stac-api-extensions.github.io).
 
 ## Structuring Catalog Hierarchies
 

fragments/itemcollection/README.md

@@ -29,7 +29,8 @@ This object describes a STAC ItemCollection. The fields `type` and `features` ar
 
 ## Extensions
 
-- The [Context Extension](https://github.com/stac-api-extensions/context) adds additional fields to STAC ItemCollection relevant 
-  to their use as search results.
-- The [Single File STAC Extension](https://github.com/stac-extensions/single-file-stac/blob/main/README.md) provides a set of Collection 
-  and Item objects as a single file catalog.
+STAC API Extensions can be found [here](https://stac-api-extensions.github.io).
+
+In addition to STAC API extensions, the STAC
+[Single File STAC Extension](https://github.com/stac-extensions/single-file-stac/blob/main/README.md)
+provides a set of Collection and Item objects as a single file catalog.

item-search/README.md

@@ -297,10 +297,4 @@ the [overview](../overview.md#example-landing-page) document.
 
 ## Extensions
 
-These extensions provide additional functionality that enhances Item Search.
-
-- [Fields Extension](https://github.com/stac-api-extensions/fields/blob/main/README.md)
-- [Sort Extension](https://github.com/stac-api-extensions/sort/blob/main/README.md)
-- [Context Extension](https://github.com/stac-api-extensions/context/blob/main/README.md)
-- [Filter Extension](https://github.com/stac-api-extensions/filter/blob/main/README.md)
-- [Query Extension](https://github.com/stac-api-extensions/query/blob/main/README.md)
+STAC API Extensions can be found at [stac-api-extensions.github.io](https://stac-api-extensions.github.io).

ogcapi-features/README.md

@@ -396,12 +396,4 @@ as is typical with a static STAC Collection, there are no links here with rel va
 
 ## Extensions
 
-These extensions provide additional functionality that enhances *STAC API - Features*.
-
-- [Transaction Extension](https://github.com/stac-api-extensions/transaction/blob/main/README.md)
-- [Items and Collections API Version Extension](https://github.com/stac-api-extensions/version/blob/main/README.md)
-- [Fields Extension](https://github.com/stac-api-extensions/fields/blob/main/README.md)
-- [Sort Extension](https://github.com/stac-api-extensions/sort/blob/main/README.md)
-- [Context Extension](https://github.com/stac-api-extensions/context/blob/main/README.md)
-- [Filter Extension](https://github.com/stac-api-extensions/filter/blob/main/README.md)
-- [Query Extension](https://github.com/stac-api-extensions/query/blob/main/README.md)
+STAC API Extensions can be found at [stac-api-extensions.github.io](https://stac-api-extensions.github.io).

overview.md

@@ -56,8 +56,8 @@ for more details.
 ### Extensions & Fragments
 
 Both STAC API and OAFeat allow 'extensions' that can be added for additional functionality. The STAC community has 
-created a number of extensions to OAFeat, in order to meet the requirements of its implementors and the complete list 
-can be found in the [extensions document](extensions.md), which links to each of them and details their maturity. 
+created [a number of extensions](https://stac-api-extensions.github.io) to OAFeat
+in order to meet the requirements of its implementors. Additional details about extensions can be found in the [extensions document](extensions.md).
 These are specified in OpenAPI, which works cleanly when the new functionality is a new API location (a complete 
 resource, or adding POST to an existing one). Many of the additions, however, are done at the parameter or response 
 level, like adding a `sortby` field to return ordered results. To make these reusable by both Item Search and OAFeat,