This will allow us to modularize message processing, e.g. having new modules to manipulate
channel and private messages in new ways.
Yes: it can be used to intercept messages, but such modules are already out in the wild for
charybdis anyway -- so this doesn't really change anything there.
If you are changing the text, then it is your responsibility to provide a pointer to a new
buffer. This buffer should be statically allocated and stored in your module's BSS segment.
We will not, and cannot, free your buffer in core, so dynamically allocated buffers will
cause a memory leak.
This will allow us to simplify m_message considerably, by moving channel mode logic out to
their own modules.
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