Fixed some XML comment issues
Improvements to SklLib/IO/ConfigFile* classes

Got rid of some "magic" strings. The characters that indicates section, key or comments can be changed by child classes.
Improved internal buffer performance. Stores sections, keys and values converted and ready to use.
Improved file validation and parse to run once.
Obsoleted IsValidFile static methods, should use instance methods.
Got rid of ugly "goto" commands, instead using anonymous methods.
Added option to trim section names, keys names and values.