[database] Move database functions to a dedicated class
[database] Allow NULL values in "nick" field

IRC messages can be written without include nicknames. For instance,
status or server messages. For those cases NULL values are allowed.
[parsers] HTML and plain text parsers for IRC log messages

The tool can parse HTML and plain text messages. These changes are
based on Marius Gedminas' irclog2html.py tool, released under
the terms of the GNU GPL. Thanks to the author for this great tool.
[analysis] Classification of IRC messages

Messages are categorized into user's COMMENTs or actions like JOIN
the channel, PART from the channel, SERVER actionsor generic
ACTIONS. Messages out of these categories are classified as OTHER.
Merge branch 'master' of https://github.com/MetricsGrimoire/IRCAnalysis

Conflicts:
	irc_analysis.py