ambertools14 (new formula)

Amber is a free-as-in-freedom molecular dynamics toolkit. Until now,
there was no homebrew distribution of Amber. Because most serious
molecular dynamics simuations are done on cluster computers rather than
macbooks, one might ask 'why bother?'. Having amber on one's own machine
is useful for prototyping something simple in an environment where one
has full control over the environment and guaranteed access. With this
in mind, the installation with default options is simple and
conservative. Parallelism and leveraging of the GPU must be explicitly
specified.

While `brew audit' considers setting environment variables in shell
commands to be bad form, using ENV simply does not work in my case. This
is my first time writing a formula, or using ruby for that matter, so I
welcome anybody's willingness to fix that messiness.
```ruby
depends_on :x11 => :optional
```

In the dependencies, which will then generate a `--with-x11` option that you can check via `build.with? "x11"` below.