Make message parsing less memory hungry

[Erik Huelsmann]

Andreas Fuchs has suggested to use displaced arrays instead of copy-seq instructions to create the different message portions. This prevents a lot of copying around of the same message content.

[Erik Huelsmann]

Partially resolved, because only normal message parsing was affected in r148. No further audit of the code was done to see if other places could be optimized.

There the isupport code and ctcp code however probably can benefit from displaced arrays too. The ISUPPORT code however is invoked only on connection startup, meaning this probably isn't worth the time.

[Erik Huelsmann]

r149 changed more code from subseq' to substring'. This completes the work meant by this issue.