Edit and colorize help verbiage

* Lots of text changes
* Abstract out similar verbiage
* Define print_colors()
* Relocate 'Known Issues' section
* Add background color examples to help
Update colorize() to treat text as a single blob

Allows for the continuation of color over whitespace
in the text message only
Add subroutine + hook for word filters

* Define modify_word()
* Change 'http' regex to include opening parens before http:
* Remove opening parens before http using filter hook
Abstract out components to global hash
Add reset colors command
Add more help command verbiage and edit existing

* Add 'Commands' section
* Change formatting of 'Examples' section
* Edit IRSSI script url and date
* Lots of small grammar and formatting changes
* Update changelog
Add README.md
Add screenshot PNG files