Avoid writing (temporarily) into source directory.
Keep git push happy.
Removed references to SunPlus.
Fixed typo.
Avoid tmpfile().

- tmpfile() tries to create files in the C: root dir on Windows where users usually don't have access.
- tmpnam() uses the curent dir which doesn't seem to be a good idea either.
- tempnam(NULL,NULL) is supposed to be cleverer.
Define _SVID_SOURCE to get tempnam().
Use -Werror only on Travis CI builds.

There's no need to intentionally break things for people trying to build cc65 with some obscure compiler. It's enough to make sure that no new warnings sneak into the code base by having Travis CI builds fail.
Switched to Markdown in order to allow to add links.
Fixed URL.
Made html doc look a little less boring.
Adjusted linuxdoc parameters.
Some minor fine tuning.
Deduct temporary library path name from library path name.

Actually there's no need to fiddle with any automatic temp file name generation as we can just modify the library path name to generate a perfect temporary library path name.
Merge remote-tracking branch 'upstream/master'