Add source encoding and literal conversion to the GnuCOBOL compiler

COBOL source files may use different encodings. Commonly, these use some 8-bit character encoding like ISO-8859-15 or an EBCDIC one "transferred as binary from the Mainframe". Newer sources are often written in UTF-8, which can pose challenges for user-defined words and literals stored as single-byte characters. The project aims to support files with different encodings and internally convert between UTF-8, UTF-16, stored as byte arrays.