* if OS environment variable $PHINX_ENVIRONMENT is set, use its value as the default environment
* update development installation instructions
* update documentation about $PHINX_ENVIRONMENT, add explicit warning about configuration files in version control
prefer $PHINX_ENVIRONMENT to all other defaults
better error message to indicate environment name is taken from shell variable
Merge tag 'v0.2.5' of github.com:robmorgan/phinx into 0.2.x-dev

Tagging release 0.2.5

Conflicts:
	README.mdown
merging in #82.