travis: use a custom travis.yml script.

Slingshot travis.yml is for testing with various Lua versions,
but Zile is Lua5.2 only, and needs to install with both LuaRocks
and with `make install`.
* bootstrap.conf (slingshot_files): Remove travis.yml.in.
* .gitignore: Remove travis.yml.in.
* travis.yml.in: New file, customised from slingshot version.
* .travis.yml: Regenerate.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
doc: start LDoc based api documentation.

* configure.ac (AC_PATH_PROG): Find a suitable ldoc.
(SS_CONFIG_TRAVIS): Add ldoc rock dependency.
* doc/config.ld: New file. List LDoc commented sources.
* local.mk (EXTRA_DIST): Add doc/config.ld.
(dist_doc_DATA, dist_classes_DATA, dist_modules_DATA): Distribute
and install LDoc documentation.
* .gitignore: Adjust.
* .travis.yml: Regenerate.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>