Add a flag to unescape variable values

[francescomari]

Fixes #639

Summary of Changes

1. Add a new router option configurabile via UnescapeVars.
2. When UnescapeVars is active, variable values are automatically unescaped when a match is found.
3. When UnescapeVars is active, variable values are automatically escaped before generating the route's URL.

[francescomari]

@elithrar I tried to fix #639 with as few changes as possible, but I figured that it would have been difficult to maintain backwards compatibility without adding another option to the Router. If you think this is not the right way to go, please provide guidance on how to proceed (or whether #639 should be fixed at all).

[francescomari]

@elithrar I have a question re. the consistency of the API. UseEncodedPath receives no arguments, but UnescapeVars does receive a boolean. Wouldn't look more consistent if UnescapeVars received no arguments, too? If called, it would just activate the flag, like UseEncodedPath does.

[elithrar]

Wouldn't look more consistent if UnescapeVars received no arguments, too? If called, it would just activate the flag, like UseEncodedPath does.

Yes, unlabeled (Go doesn't have labelled args), single Boolean arguments are a bit of an anti-pattern.

[francescomari]

I've removed the flag. Now UnescapeVars just set the flag as true under the hood.

[stale]

This issue has been automatically marked as stale because it hasn't seen a recent update. It'll be automatically closed in a few days.