Set X-Forwarded-Port header to fix rack middleware

Rack middleware currently generates incorrect URLs when serving an app
through pow with this module. During a request to `http://myapp.pow`,
calling `Rack::Request#url` produces `http://myapp.pow:30559`.

Rack is incorrectly using the port that pow is listening for proxied
connections on. This header tells rack what the original port that the
end user connected to was, which lets it generate the right URLs.
fix(powconfig) Fix the template for powconfig. Now removes  whitespace from domains variables
fix(docs) typo
fix(nginx) Sets X-Forwared-Host header to fix omniauth redirect mismatch
Merge pull request #11 from platanus/fix-whitespace-in-domains

Removes  whitespace from domains variables in .powconfig
Merge pull request #12 from platanus/docs

fix(docs) typo in the Readme
Merge pull request #10 from eugeneius/x_forwarded_port_header

Set X-Forwarded-Port header to fix rack middleware
Merge pull request #13 from platanus/x_forwarded_host_header

fix(nginx) Sets X-Forwared-Host header to fix omniauth redirect mismatch