chore(readme): 2020 announcement

Fixed the comment about the return value for snprintf and vsnprintf (issue #45)

chore(readme): fixed space

test(test_suite): added support for PRINTF_DISABLE_SUPPORT_EXPONENTIAL

chore(printf): minor cleanup

test(test_suite): added more float test cases

chore(readme): update readme to exp support

chore(catch): update to catch2 2.7.0

chore(readme): added the Hatchling platform as using project

feat(printf): added vprintf() support

chore(printf, test_suite): clean up

Merge exponential support

Implemented custom log10/pow in _etoa to eliminate dependency on <math.h> for %E format

Fixed whitespace, added %e/%g to README.md

Added special-case handling to %E, added +inf and -inf handling, test cases