changed the version number to __GITHUB__ (the github version is not a release)
fixed a spurious 'notice' when used as library
added a LAYOUT option

use @define(LAYOUT,{'table','list','deflist'}) to choose between table, ul, ol ('list' and ABBRV_TYPE='index') and definition lists for displaying bibtex entries.

$bib->index is now displayed as a number, not a number in brackets, for compatibility with list values. however this is invisible to the user because the brackets are added in getAbbrv().

bib2html now includes the echoing of links.
refactored the excellent commit of M. Guillaumin

- LAYOUT -> BIBTEXBROWSER_LAYOUT by convention
- BIBTEXBROWSER_LAYOUT has non-abbreviated values (for sake of intuitiveness)
- BIBTEXBROWSER_LAYOUT has no complex interplay with ABBRV_TYPE  (for sake of intuitiveness)
- ordered lists are responsible for the indices
- no new line at the end of the file
- renamed or moved some functions