new method for getting the content in the file FileGetContents

[marineusde]

That do some problems in unit tests, cause you cant mock or fake the schema files. The content getter is separated now to override it, if someone use test frameworks.

[DannyvdSluijs]

Hi @marineusde

Thanks for your contribution. I do have some questions regarding this PR.

1. Can you explain this PR a bit better? What is it solving, how is it solving it. Some examples would greatly help in understanding these changes.

2. I'm curious why you're reverting a fix made in Addresses Content-Type mismatch on HTTP 301 Moved Permanently with FileGetContents #709 without addressing the why?

[marineusde]

Hi @marineusde

Thanks for your contribution. I do have some questions regarding this PR.

1. Can you explain this PR a bit better? What is it solving, how is it solving it.  Some examples would greatly help in understanding these changes.

2. I'm curious why you're reverting a fix made in [Addresses Content-Type mismatch on HTTP 301 Moved Permanently with FileGetContents #709](https://github.com/jsonrainbow/json-schema/pull/709)  without addressing the why?

Sorry! I explain it in the issue, dont know why github doesnt linked it here:

#734

I dont want to revert anything, I just want to split the code for getting the content in a different method.

[DannyvdSluijs]

As mentioned in #734 I highly recommend implementing your own version of the required interface.