Update readme to include fixes for rails 3.2.x.

Rails ignores the database.yml when DATABASE_URL is defined, but rails 3.2.x does not correctly parse `prepared_statements=false`.

prepared_statements=false is evaluated to `{prepared_statements: "false"}`, rather than `{prepared_statements: false}`. The string `"false"` evaluates to true, so prepared statements are not disabled correctly.

The monkey patch filters the config options hash, and correctly maps the `"false"` to `false`.
Adding support for logging related variables
Add stats_period to the available config vars
Add new logging vars to readme
Merge pull request #9 from jhorman/less_logging

Environment variables to control pgbouncer logging
README fixes for clairity
Add PGBOUNCER_MAX_CLIENT_CONN to the heroku config
Merge pull request #11 from khamaileon/master

Add PGBOUNCER_MAX_CLIENT_CONN to the heroku config
Use MD5 hashed password in users.txt
Set stunnel dir perms go-rwx
Generate config files in start-pgbouncer-stunnel script

This change moves the generation of config files out of the profile.d
dir and into the start script. This allows over rides of config vars to
at config generation time.

Fixes #13
Update README
Gen config files before overriding config vars
Merge pull request #14 from gregburek/config-gen

Generate config in start script and use md5 passwords
Change copy based on @gregburek's feedback
Merge pull request #7 from ms-digital-labs/readme-update-for-rails-3-2

Update readme to include fixes for rails 3.2.x.