Improve security in string operations, add option to directly read a color file

[pinballpower]

• use str*_s functions if available or a simple implementation of these if the comüpiler doesn't provide these
• add some constants in header file
• add Serum_LoadFile function that doesn't require a ROM directory, but uses a plan file name. File can be either a compressed .crz file or an uncompressed .cROM file