Add rbenv default-gems file

- Adds a list of default gems in ~/.rbenv/default-gems

see:
https://github.com/sstephenson/rbenv-default-gems
Add Ruby optimizations

Optimization Flags
==================

You may not know that neither rbenv nor RVM passes any optimization
flags to the compiler when it builds Ruby.

A very simple way to get a small bump in performance is to do that:

$ CC="clang" CXX="clang++" CFLAGS="-march=native -Os" rbenv install 1.9.3-p327

-Os optimizes for size. On modern processors, this is often better than
-O3 because a smaller code footprint gets more code into the CPU caches.
(If you look at the default release optimization level for a new Xcode
project, you’ll find that Apple agrees with me.)

-march=native tells the compiler to tune the code it produces for the
CPU on your machine. This is good for situations like this, where
you’re only running the Ruby binary on the machine that built it, but
it shouldn’t be used for code you distribute to others. There is a
catch, though: rbenv usually uses GCC, but the version of GCC
distributed by Apple doesn’t know about -march=native. Clang does.
A Clang-built Ruby knows to use Clang for gem native extensions, too.
Even though Ruby itself isn’t C++, a gem might use it, which is why you
must set both CC and CXX.

Tune the Garbage Collector
==========================

Similar to Ruby Enterprise Edition, you can tune the garbage collector
to run less frequently at the expense of larger Ruby processes. The
argument goes that 10 faster, larger processes are better than 20
slower, smaller processes.

Set these environment variables in your ~/.bash_profile.

export RUBY_GC_MALLOC_LIMIT=60000000
export RUBY_GC_HEAP_FREE_SLOTS=200000
Add gh to laptop.local
Update vim bundles list
Lint README and gvimrc.local
Add e() to open vim with cwd set to destination
Update vimrc