fails to recognise stdint types

[arnetheduck]

types like uint64_t and friends have direct correspondents in Nim (uint64) - this should be recognised and translated accordingly.

[elcritch]

This is possible with the mangle option that was merged recently: --mangle:'{u?}int{\d+}_t=$1int$2'.

However, my new PR includes a --stdints to set this up automatically. See: #251

[elcritch]

@Araq I believe this can be closed now with #251.