First commit of the BibTeX format support, thanks to Oyvind. The changes notably are:

• Added HX (=HTML BibTeX) behaviour, to be called on the fly.
• Added HX format to the format table, and renamed some existing formats (e.g. MARCXML instead of XML MARC). Note to self: the formatname table is to be prefilled if we want to have full I18N format names.
• Added _FULL_BIBTEX format to the flxFORMATS table, in a monolithic form. The `non-standard' fields such as URL, abstract, eprint number, etc are to be studied and the treatment refined (e.g. journal page numbers versus report numbers). Also, the monolithic form of this format is not admin-friendly, to be refactored or possibly pybliographerized.
• Added KB demo values for the mapping of tag 980 values to the BibTeX entry types.
• Added four supporting UDFs (STR_BUFFER, GET_NAME, SPLIT_LINE, GET_MONTH, GET_YEAR). May come handy independently of BibTeX.