Put all commands in different functions. This is hopefully a little bit
clearer arranged and it make it easier to start the same command from
different buffers by the präfix /ircrypt and from the ircrypt buffer
without präfix. Also handle spaces in keys, asymmetric identifier and in
special ciphers. Moreover add and change some docstrings and  change
weechat.prnt output (only minor things). Related to #19, #25 and #28.

Signed-off-by: Sven Haardiek <Sven@Haardiek.de>