* created new decoder and encoder for PFM

pfm file format stores binary RGB or grayscale float images.

* added test for pfm codec

* replaced large with short licence header

* little/big-endian-check is now compile time

* fixed width/height confusion, improved big/little endian recognition, fixed scaling issue and Improved signature check

* adapted tests to handle float images well

* removed data-dependency: lena.pfm

the lena image is now loaded is pam and converted to pfm.

* fixed bug in endianess detection macro

* Added endianess detection for android and win

* removed fancy endianess detection

endianess detection will be implemented in cmake scripts soonish.

* fixed minor warnings

* fixed stupid elif defined bug

* silenced some implicit cast warnings

* replaced std::to_string with std::stringstream solution

std::to_string variant did not build on android.

* replaced new endianess macros with existing ones

* improved readability