Add support for '_' as a digit separator in numbers.
Add support for '_' as a digit separator in numbers.

skystrife/cpptoml,Payshare/cpptoml,Payshares/cpptoml,skystrife/cpptoml,vadz/cpptoml,Nephatrine/cpptoml,Nephatrine/cpptoml,vadz/cpptoml,zzzworm/cpptoml