Minor updates

Hey all, I've updated how strings are defined in the help file and in the compiler.  They default to CBM screen codes, but you can use ascii or petscii instead of string to use the corresponding character types instead.

I've also added another BBC example, a hello world one.

ps. Sometimes the compiler locks up when generating output files, unsure why at this point, so make sure you save your work prior to compiling/running the programs!

Hope you enjoy!