Enable build warnings/errors on Windows

[kou]

src/h3lib/lib/coodijk.c:

(73,10): warning C4244: '=': conversion from 'double' to 'int', possible loss of data
(74,10): warning C4244: '=': conversion from 'double' to 'int', possible loss of data
(133,25): warning C4244: '=': conversion from 'double' to 'int', possible loss of data
(137,25): warning C4244: '=': conversion from 'double' to 'int', possible loss of data
(236,13): warning C4307: '+': signed integral constant overflow

src/h3lib/lib/localij.c:

(633,14): warning C4244: 'initializing': conversion from 'double' to 'int', possible loss of data
(634,14): warning C4244: 'initializing': conversion from 'double' to 'int', possible loss of data
(635,14): warning C4244: 'initializing': conversion from 'double' to 'int', possible loss of data

src/apps/testapps/testH3Memory.c:

(84,21): warning C4098: 'test_prefix_free': 'void' function returning a value

src/apps/testapps/testMathExtensionsInternal.c:

(81,9): warning C4307: '-': signed integral constant overflow
(82,9): warning C4307: '-': signed integral constant overflow
(83,9): warning C4307: '-': signed integral constant overflow
(84,9): warning C4307: '-': signed integral constant overflow
(85,9): warning C4307: '-': signed integral constant overflow
(86,9): warning C4307: '-': signed integral constant overflow
(87,9): warning C4307: '-': signed integral constant overflow
(88,9): warning C4307: '-': signed integral constant overflow
(89,9): warning C4307: '-': signed integral constant overflow
(90,9): warning C4307: '-': signed integral constant overflow
(91,9): warning C4307: '-': signed integral constant overflow
(92,9): warning C4307: '-': signed integral constant overflow
(93,9): warning C4307: '-': signed integral constant overflow
(94,9): warning C4307: '-': signed integral constant overflow
(95,9): warning C4307: '-': signed integral constant overflow
(96,9): warning C4307: '-': signed integral constant overflow
(97,9): warning C4307: '-': signed integral constant overflow
(98,9): warning C4307: '-': signed integral constant overflow
(99,9): warning C4307: '-': signed integral constant overflow
(100,9): warning C4307: '-': signed integral constant overflow
(101,9): warning C4307: '-': signed integral constant overflow
(102,9): warning C4307: '-': signed integral constant overflow
(103,9): warning C4307: '-': signed integral constant overflow
(104,9): warning C4307: '-': signed integral constant overflow
(105,9): warning C4307: '-': signed integral constant overflow
(106,9): warning C4307: '-': signed integral constant overflow

src/apps/testapps/testCellToLocalIj.c:

(204,44): warning C4146: unary minus operator applied to unsigned type, result still unsigned

[coveralls]

coverage: 98.824% (-0.003%) from 98.827% when pulling 5a6cea4c368532228fc906002653c254e341f873 on kou:windows-warning into afaa41a64f13e97c37ecc692fa6eec7a7e721680 on uber:master.

[isaacbrodsky]

Thanks for adding warnings-on-Windows! I'm not entirely certain why coveralls is reporting coverage fell, it might be because of changing the macro to an inline function.