Remove quotes from defined words

[JeromeMartinez]

From Barry Leiba's Discuss:

General: It’s jarring to see the defined terms, such as “Sample” and “Pixel” in
quotes every time they’re used. More common practice is to quote them when
they’re first defined, and then to just use the capitalization to show that
they’re defined terms. I find that the quotes affect the readability and make
it somewhat more of a challenge to read.

So I removed quotes from defined words.
As Frame is not only a defined word but also a part of the bitstream, it is not just a find and replace, so maybe some double check to do.

I also added the missing definition of Line.

[michaelni]

Does not apply cleanly to master/HEAD anymore "This branch has conflicts that must be resolved"

[JeromeMartinez]

PR udpated for including changes from #238, no more conflicts.