Faster _CustomWriteIntUnrolledSigned

Tested across integers of all lengths this was between 90-95% of the
time of the original (sweet spots were at 3/6/9 which were 75%,91%,94%
and worst spot was 5 digits which was 102%). Adds buffer that is "1000 *
3 * sizeof(char)".
Better _CustomWriteIntUnrolledSigned

Only write the required digits
Removed unnecessary modulus operations

Argh! I'm obsessed with this function!!
Merge branch 'write-int' of https://github.com/manofstick/Jil into issue-54
test for #54; it does appear to be 10-15% faster, may also obsolete SkipNumberFormatting
cleanup code; remove a switch I'd rather not stick around
skipping number formatting is done within CustomWriteInt now; no longer a relevant switch or test, removing
extend DigitTriplets to CustomWriteUIntUnrolled
upgrade to Sigil 4.2.2
2.0.2
Merge remote-tracking branch 'upstream/master'