It finally works now
Definitely some clean up to be done

Currently writes IHDR and IEND chunks correctly
CRC implementation is borrowed from the specification
Writer class now also has a buffer for the CRC calculation

Also moved both the reader and writer class to the same files, named
files.{cpp,h}

Currently not incredibly well implemented, but it can handle fixed
codes

The file reader class can now support either endianness to read in,
and will convert to the native endianness

All functions and classes are now behind the cpp namespace `TehImage`

Had to restrict images to 8 bit depth sadly
This could potentially be changed in the future by setting bit depth
with templates and changing the data to be the specified bit depth

the average filter method

Mainly just cleaning up code

Also added the bitmap image subclass
note: this is pretty hacky in how it works