Add filepath to replacement callback

[ianstarz]

This adds access to the file path within the replacement hook for replace operations that are based on conventional directory structures

[oleggromov]

👍 for this feature, it is useful.

[lazd]

This PR does not seem to support regex search and replace for this feature. If you can find a way to support that (using replace.bind() maybe?) then I think we can go forward with it, but we need feature parity between normal search/replace and regex for this to go in.

Also, docs and tests please! :)

[oleggromov]

Lazd, the replacement function can also be called from within the replacestream library call, thus, for consistency, the fix should involve the streamed input too, doesn't it? The problem is in creating inconsistency on the other side: replacestream calls the replace function with a different bunch of arguments (just like String.prototype.replace calls its arguments of type function; details can be found in readme) while gulp-replace is going to introduce its own format.

How do you think should this issue be solved?

[oleggromov]

I made a correct and consistent for all use cases fix in a sibling PR: #67
Please take a look.

[ianstarz]

Thanks @oleggromov, closing in favor of #67