should not use [ ] when condition is a command

- add .travis.yml
- update Makefile to make it work with travis CI.
- add requirements.txt file
- bugfix: "make dist-check" should use ert-run-tests-batch-and-exit

sometimes after GetCandidate dbus call, zero-input-fetch-size and
zero-input-candidates is not updated. This was because the async
function callback didn't update the metadata in some places.

- update initial fetch size and fetch size to be 1+ candidates needed for
  target page.
- removed zero-input-build-candidates-complete function,
  each async call should have its own callback function, don't reuse this one.
  in callback function, post GetCandidate metadata should be updated.

since this is a backward incompatible change, I set version to v2.0.0.
all symbols and functions is now prefixed with zero-input.

This change is suggested by melpa reviewer.

- renamed zero.el back to zero-framework.el
- to build a dist, just run "make".
  the zero.el template is in zero.el.in
- zero.el is built and added to git repo in git pre-commit hook. it will
  be kept in master branch.
- fixed a few package-lint style warning.

split ert tests to separate files. These tests are not required in melpa
distribution.

- fix almost all checkdoc problems. the rest I don't know how to fix.
- add git pre-commit hook

- merge lexical-binding line with file intro line
- allow capitalize zero in some docstring/error msg
- add "make pkg" this will create tar for package.el

added "make compile" to byte-compile and run tests in emacs batch mode.