Add BibLaTeX snippets and parenthesis snippet

Signed-off-by: Rene Vergara <rene.a.vergara@gmail.com>
Add a snippet for BibLaTeX for book, inbook, online and article.

Add a snippet for LaTeX to enter a parenthesis pair.
Add snippet for ledger

Signed-off-by: Rene Vergara <rene.a.vergara@gmail.com>
Add a snippet to enter a transaction into a ledger file to be
used with the ledger accounting tool.

Recommend to use the vim-ledger plugin for filetype detection.