Use more stdint.h types

[magv]

Use stdint.h instead of INT{16,32,64}. Make WORD always int32_t, and drop ILP32 support. As discussed in #670. ILP32 deprecation was previously suggested in #624.

[magv]

I guess because of all the LONG <-> pointer conversions in the code, LONG should really be the same as intptr_t (unless the conversions are fixed), which makes compilation on 32-bit systems broken if WORD/LONG are 32/64 bits.

[coveralls]

coverage: 50.594% (-0.009%) from 50.603%
when pulling 50d4bdc on magv:stdint
into 21f29a8 on form-dev:master.

[magv]

OK, so this is the current proposed set of changes to use stdint.h more. This is what was discussed in @670, except I've decided not to remove ILP32 support for not, because it turned out to be very helpful in catching WORD vs int distinction in the code (something I'd wish the compiler would do for us, but it wouldn't). Instead I've slightly simplified the detection of 32-bit platforms using stdint.h alone, and updated all the code that did #ifdef ILP32 to #if BITSINWORD == 16. I would, of course, still support deprecating the 32-bit support, but keeping the (minimal set of) tests for it running would still be beneficial.

[jodavies]

This cleanup looks good to me. Any comments from anyone else?

[tueda]

If I'm not mistaken, off_t is 32 bits in 64-bit MSVC, but it may be OK to remove the large file support warning (anyway there would be more issues for LLP64 and no one cares).