Move string functionality to rp_string.h
Move utils into static library

* Should help with writing tests.
Move IRC state-machine parser to library

* Should allow for unit testing in the future.
Clean up ircsm code

* Use a shared buffer for hostmask and servername prefixes in an IRC
  message.
* Rename prefixes rp_irc_sm to rp_ircsm.
* Fix leading space in params.
* Write a parsing test application to test the message state machine.
Add new string functionality

* Implement rp_strtoken, a tokenizer function.
* Implement rp_strstr, a strstr implementation for rp_str_t.