Update to Julia v0.7

[RalphAS]

Here is package test output from 0.7-beta (omitting lots of deprecations):

Test Summary:	Pass	Fail	Error	Total
AxisArrays	140	12	14	166
Core			1	1
Intervals	60		60
Indexing	19		5	24
SortedVector	3	7		10
CategoricalVector	4	4	3	11
Search	26			26
Combine	28		4	32
README			1	1

Also, are users now expected to module-qualify all calls of axes (since Base exports an incompatible function)?

(Sorry to ping you, @mbauman, but this repo doesn't seem to get much attention and the last question is important for the image-processing ecosystem.)

[tlnagy]

Bump. Also @timholy?

[mbauman]

I'll try to get to this shortly! Sorry for letting it sit for so long.

There are so many new goodies in 0.7 that AxisArrays will want to take advantage of, but that's much lower priority.

[mbauman]

Fixed by #143