Run_Width() Improvements + General Cleanups

Removed expired Compress() code
Run_Width():
The first character is no longer treated differently, improving
compression
Added some small comments
Values 255 and over are now properly dealt with: A 255 character is
inserted in their place, and 255 is subtracted from the value. The
remainder is then placed afterwards, after checking it is not also 255
or over (in which case the process repeats).
Tweaked error-checking with custom error message
Double-zeroes now correspond to EOF

Cleaned up Test_DCT() and added a new test subject
Cleaned up Run_Width() significantly and added a test case for values
over 255