Lexer: Remove unused CC_STR_NEWLINE and CC_STR_EOF.
Simplify line scanning.

There are currently three line scanning handlers: One for files, one for
strings, and one in apache for the apache file. These changes apply to all of
them:

* If a \r is seen, rewrite it to \n. Additionally, \r\n is now seen as \n.
  This was done because, otherwise, a multi-line string could have different
  values depending on the newlines written by the editor. Python seems to do
  the same thing.

* Do the realloc check in one place, and use i + 1 == size now that \r\n is
  no longer added.
The lexer can now enter multiple sources.

Previously, the lexer allowed trying to enter a file/string/other after
something was already entered. However, doing so would result in a crash.

Unfortunately, this isn't an import mechanism, but it's a critical part OF an
import mechanism (so that's a plus). I did this in part because it's needed
for #68.

Additionally, a decision has been made that will be important in the future:
The lexer will only honor the mode of the first file entered, and enforce a
no-tags policy on entered files. For now, this is to allow the parser to load
tagless things (when I to #68) without having to save/restore the mode.

For now, this is just about adding a mechanism which will do nifty things in
the future, but nothing right now.