Major improvements to documentation & filters

• Add documentation for all filters
• Refine many filters to be more unicode compatible, cover more use cases, or be more efficient (less regex)
• Adjusts tests to remain at 100% coverage

v0.7.1: Improve NormalizeLettersToAscii & add new filters

- Make very intense tests about the characters which should
  be converted in NormalizeLettersToAsciiFilter and add many
  additional conversions to have better and more complete
  results
- Add RemoveEmailsFilter and RemoveURLsFilter
- Rename the "Manager" tests to "Selector" tests to be consistent

Rename some classes

Rename selector classes (were "manager" classes before) and rename one filter

v0.6: Put debug functionality in its own packages

squirrelphp/debug is now used for all exception and debug
functionality, so we do not need to replicate it for every
squirrel component.

v0.5

First official release