remove zsh completions

reason: as discussed in #244, the completion file was moved to
https://github.com/zsh-users/zsh-completions
Merge branch 'remove-zsh-completions'
Remove Emacs 23 from Travis
Add Emacs 24.4 to Travis
Delete stale lock file
[Fix #261] Remove pointless installation warning
dsl.rst: Fix case for Org mode archive
Merge branch 'fix-org-archive-case'
Remove text about el-get
Improve fetcher dependency docs

That is the docs for the DSL function depends-on.