chore: rename some ports and generics to better match function

chore: add documentation to the code

fix(link): make testbenches work in quartus, fix old testbenches

feat(link): output frame_character from data link, add user_data to character

feat(link): use character_vector in 8b10b decoder

fix(link): decode control characters correctly. Correctly check for missing disparity

feat(link): add 8b10b decoder