Split mail splitting and processing into separate methods.

This allows the splitting to be done independently from the processing.
Add a possibility to use rb-inotify for automatically preprocessing new mails.

This puts a much leighter strain on the system compared to periodically
checkign ALL the mails. The HTML conversion however is carried out by
MHonArc on a periodic basis anyway so this can’t be inotified.
Add a primitive search function.

Really, this is primitive. It search the convert HTML (!) by opening
all the mails and checking their contents... It would really be
better to dedicate this task to something like Lucene (but that
is Java...). Also, one shouldn’t search the HTML, but rather the
original mail sources, but sadly, there’s no way to map the email
source file names to the resulting HTML file names apart from
opening up **all** HTML files and checking for the message ID you
previously have to read from the email sourcefile which of course
has to be parsed previously. Improvements welcome.