Closes #809, references #806

This is for Linux desktop platforms that have Terminal application
configured to start shells in interactive but not login mode. Creating a
`~/.bash_profile` would also cause `~/.profile` to not run, which might
be a problem on Ubuntu which ships with a default `~/.profile`.

Avoid running `rbenv rehash` multiple times during `bundle install`

This avoids running `rbenv rehash` after installing libraries that don't
have executables, or after a no-op `bundle install` that didn't install
anything.

This is an attempt to work around the fact that Rubygems post_install
hooks may happen multiple times per single `bundle install` and ideally
we want `rbenv rehash` to run only once if new gems have been installed.
However, due to Bundler parallelism using `fork` on platforms that
support it, it's impossible for the child processes to communicate with
the master process to signal it to run `rbenv rehash` in the end.

This hooks into Bundler `install` command and runs `rbenv rehash` after
all gems have finished installing, but only if the install location was
system gems location and not a custom path (such as per-project
`vendor/bundle`).

This is limited because we can't tell whether any gems have been
installed at all, let alone do those gems have executables. However it's
better than having multiple `rbenv rehash` being run in parallel and
outputting confusing error messages as a result.

When `rbenv --version` is called, this now happens:

1. It changes into the directory where `libexec/rbenv--version` resides
   and checks if it's a checkout of the rbenv repo (as opposed to
   Homebrew checkout or something else). Then it reads the git revision.

2. If that failed, change to `$RBENV_ROOT` directory and repeat step 1.

http://fwierzbicki.blogspot.co.uk/2015/10/jython-271-beta2-released.html

Use `command` to run rbenv rehash

Closes #529

If set by the user's environment, `git config --global` writes will go
to that destination instead of temporary $HOME. We definitely don't want
that.

Fixes #742

rbenv-init: do not use basename for $shell

Include gems dir in .gitignore

add proxy usage note

Add a Gitter chat badge to README.md

Closes #440

Closes #725

Fixed anaconda3 repo's paths. #438

Add CPython 3.5.0rc4

Add miniconda-3.16.0 and miniconda3-3.16.0

Will add portable when squeaky-pl/portable-pypy#17 is closed.