WGLC editorial pass

A couple nitpicky things that jumped out at me in another readthrough.

  - 3.2.1:  Says that the SETTINGS parameters don't need defaults because of HTTP2-Settings, but they *have* defaults.  Removing this claim.
  - 3.3:  Says that ALPN is used for HTTPS *if* you don't have prior knowledge, but 3.4 says you have to use ALPN even if you do have prior knowledge.  Removing the caveat in 3.3 to reconcile.
  - 5.1:  Allowing WINDOW_UPDATE to be send in reserved (remote) state.  This has been discussed in-person and on-list as a reasonable client strategy (low initial window, unchoke the pushes you want), but per the current text this is actually prohibited until after receiving the HEADERS frame.
  - 5.2.1:  Fixing sentence fragment.
  - 5.3.2:  Possibly just a personal/regional style, but from/to or between/and works for me; between/to doesn't.
  - 6.1 and 6.2 use different definitions of the padding field.  Copied 6.1's to 6.2.