Modify ConfigValueLocation to use URL instead of String

[jcazevedo]

As suggested by @derekmorr in #178, this PR modifies ConfigValueLocation to use Path instead of String to encode the location of failures.

[derekmorr]

This looks good to me, but @leifwickland raised some concerns in #178 (comment)

[coveralls]

Coverage increased (+0.2%) to 71.461% when pulling a04d882 on jcazevedo:config-value-location-use-path into 721603b on melrief:master.

[jcazevedo]

I've modified ConfigValueLocation to use URL instead of Path, in order to be able to encode the location of configuration files inside .jar files.

[coveralls]

Coverage remained the same at 71.233% when pulling 582b2b1 on jcazevedo:config-value-location-use-path into 721603b on melrief:master.

[derekmorr]

Path should be able to handle files in a jar file, but arguable using URL is better since ConfigFactory can load files from URLs.

[melrief]

I prefer URL because a URL can identify any resource in the system and can be used for locations that are not necessarily files.

[melrief]

Looks good to me

[jcazevedo]

Since ConfigOrigin has url defined in cases where filename is null, I also think we're better off with URL.

[melrief]

I approved this, let's wait for another approval and merge.

[derekmorr]

Approved.