Enhancements including help text, enforcing lynx to be present, and proper install of R15B03-1

* Extracted list_available_erl_versions method.
* Migrating egrep to grep -P. See [http://stackoverflow.com/a/7017787/1216965]
  * egrep didn't work on Mac OS X. Hence, this change.
* Refactor ~/.evm to $EVM_HOME
* Installation of evm scripts will fail if lynx is not found,
* Adding help text which will describe general usage besides additional information such as
 * EVM Home
 * Default Version
 * Versions Cached For Usage
* R15B03-1 gets installed as R15B03 which evm is not able to use / install / default, etc.