Optimise _eat_space and _get_token

Optimise _eat_space and _get_token

Makes the code more readable and has a smaller number of memory
accesses thus it's small optimisation as well.

For _get_token() optimize number parsing. Check for '.' char only
if it's not a digit. Move pointer incrementation into one place.

For _eat_space() check only p->te for '\0' in skipping of comment line.
Avoid check for '\0' when we know it is space. Also master while loop
doesn't need checking p->tb for '\0'. We just need to check p->tb
isn't already at the end of buffer. This could give 'extra' loop cycle
if we are already there - but safes memory access in every other case.