Added bash support for completion of full command line
make `shell` return an error code in case of failure

Fixes #274
Don't include `system` in `rbenv versions --bare` output
Fix `rbenv prefix` for `system` version

Should be `/usr` or `/usr/local`, not `/usr/bin` or `/usr/local/bin`
foundation for a help system where each command holds its own docs

Docs are comprised from "Usage", "Summary" and "Help" sections, where
"Help" can span multiple commented lines. If it is missing, "Summary" is
shown in its place.

References #204, references #206
use `typeset` instead of `local` in rbenv() function

This is to insure portability to ksh.

Fixes #205, references #209
Tweak `rbenv --version` output
use ruby-build

Fixes #294
Fall back to $PWD if a local version file can't be found in $RBENV_DIR
When the ruby shim is invoked with a script, set RBENV_DIR to the script's dirname
Ensure outdated shims are removed first when rehashing
Speed up rbenv-rehash with a simpler indexing approach
Run `hash -r` after `rbenv rehash` when shell integration is enabled

Fixes #119
Merge pull request #299 from sstephenson/automatic-local-exec

Automatic local exec
Merge remote-tracking branch 'griff/morecompletion'
Add zsh support for completion of full command line
avoid prepending system ruby to PATH

System ruby is already on PATH (that's the definition of system ruby) and by
duplicating its path by putting it in front, we can break the user's
environment.

Fixes #275
Merge branch 'master' into help
Improve syntax for inline documentation and allow for multi-line usage
Add `rbenv help --usage`