Corrected issues with sed reserved characters

[bkraul]

Corrected issues with sed reserved characters

This was causing the TARGET_SERVER to perform incorrect sed substitution. Fixed it by using a different separator , instead of the /. This means that paths can now be directly entered into the TARGET_SERVER variable, as such:

TARGET_SERVER=0.0.0.0:000/path

Added path filtering

On some instances, such as it is the case with Plex, proxying into a path is not enough, because the http files have the path hardcoded. Adding a filter block allows for those URLs to be rewritten in the response, allowing the assets to be loaded correctly. There might be some tweaks to make here, but the initial implementation seems to be working.

In order to use the functionality, a path must be used in TARGET_SERVER and the FILTER_PATH variable must be set to 1 (this is a safeguard, to ensure filtering is not done by default).

A new TARGET_SERVER URL-parsing block has been added to start.sh it can successfully dissect every part of the URL allowing for better future substitutions if needed. I am only using the path parsing part of it at the moment.

Other changes

Removed the HTTP_PATH variable, as it can now be extracted from the TARGET_SERVER parsing block.

[bkraul]

Closes #1