Save doc comments in the token table.

[typeswitch-dev]

Doc comments annotate the following atom, usually some kind of a definition:

||| This is a doc comment.
def(bar, ..., ...)

Right now these are discarded in the lexer. Instead they should either be saved as a token, or stored as part of the following token. Importantly, multiple doc comment lines ought to be combined (while preserving the lines), e.g.

||| Line 1 of doc comment
||| Line 2 of doc comment
def(my-word, ..., ...)