bongo-mpg123-process-filter: Improve performance

High CPU load is produced by parsing mpg123 process output.  Instead
of creating a temporary buffer for each process output and using
buffer-search/regex functions to parse it, transform input string to
an intermediate list representation by using faster string functions.

Also remove duplicate events: By rounding the elapsed time to full
seconds a lot of events don't have to be processed.

This reduces CPU load from 60% to 24% on my Core2Duo system.
Use functions instead of eval to compute track info strings
only update player times once in a second

Previously the current track line and mode line was updated every time
output was received from the player back-end process.

This reduces CPU load from 24% to 12% on my Core2Duo system.
Fixed errors and warnings reported by makeinfo
Remove `LAST-UPDATED' from `bongo.texinfo'
Use `load-file-name' instead of `find-library-name'
Add bongo-pkg.el (for `M-x package-install' support)
Simplify headers, remove unneccesary files
Drop support for Emacs 21
Delete obsolete functions and variables
Move `etc/' to `images/'
Move `bongo.texinfo' to `bongo.texi'
Move `contrib/tree-from-tags.rb' into root directory
Move `README.rdoc' to `README' and remove markup
Add simple `afplay' backend (for OS X)
Update NEWS
Add autoloads to the most common entrypoints