First phase of number to integer conversion

[pjsg]

Fixes #3214, #3215.

• This PR is for the dev branch rather than for master.
• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• The code changes are reflected in the documentation at docs/*.

Changing calls to checknumber and pushnumber to be checkinteger and pushinteger as this is (nearly always) the right thing to do.

[nwf]

These all look fine.

[TerryE]

We've also missed a few other modules:

• mcp4725.c has 4 × lua_tonumber(L, -1) replaced by (uint16) lua_tointeger(L, -1)
• rtcfifo.c has 2 × lua_tonumber(L, -1) replaced by (uint32_t) lua_tointeger(L, -1) and 2 ditto but without the coercion.

[TerryE]

@pjsg, I've gone through the rest of the updates and done another push. There's a conflict in app/modules/sjson.c but I'd like you to review this anyway so you may as well fix this via the web editor. Thankis Terry

[pjsg]

I've resolved the conflict in sjson.c -- it builds with both 5.1 and 5.3 versions. But no testing beyond that. I'll merge this into my iot device build and give it a whirl.

[TerryE]

Thanks Philip. Like you, all I did was a full Travis clean compile on both versions. I don't have the H/W to test a lot of these, but the changes are mainly number to integer swaps when the C-side variables are ints anyway.

[TerryE]

@nwf Nathaniel, perhaps you could do a review of these and merge them into dev. Thanks

[TerryE]

Just winding you up 😉. Make the change.

[TerryE]

Phil's last change fixed @nwf 's niggle so I reckon that we are good to go on this.