add more string functions

index-of, upper-case, lower-case, capitalize, trim, triml, trimr
initial character literal support
remove unnecessary unicode casts
fix compilation

that this was so difficult to track down is an issue with rpython.
trying to fix that next. (thanks #pypy!)
add character literal tests
add pixie.string/split

somehow the `.split` method on strings doesn't work here, so we have to
use the rstring module directly.
Merge pull request #41 from heyLu/more-strings

More strings functions and character literals