\a, \b, \f, \n, \r, \t, \v

not sure why those happened

for c99 compatibility

best fit for a single-header thing

not strictly necessary, but for consistency's sake

makes a lot more sense that way

added SIMPLE_OPT_CHAR, SIMPLE_OPT_DOUBLE, and SIMPLE_OPT_STRING_SET
types

also clean up integer parsing and usage printing

was an idiot and removed before, second-guessing myself -_-