Implement the support to t:parityEven7bit into libmodsecurity

[zimmerle]

Transformation parityEven7bit needs to be implemented inside libmodsecurity.

The documentation of the transformation can be found here:
https://github.com/SpiderLabs/ModSecurity/wiki/Reference-Manual#parityEven7bit

The file already exist in the repository:
https://github.com/SpiderLabs/ModSecurity/blob/libmodsecurity/src/actions/transformations/parity_even_7bit.cc

[zimmerle]

Implemented.