Support for non XCTest subsclasses about swiftymocky

[amichnia]

Add other platforms support (max os, tv os ...)

[amichnia]

We can separate it completely, using subspecs. It would look like:

1. Define MockyAssert instead of using XCTAssert
2. Define subspecs as following:

• core (default): depends on XCTest, MockyAssert is type alias for XCTAssert
• inapp: MockyAssert is plain assert
• nimble: MockyAssert wraps Nimble expect (?)

There are few caveats here:

• when not default subspec, CocoaPods does not contain other files, like templates etc - we can probably define them as assets

[amichnia]

for now, there is one additional Custom pod spec. It allows to override how assertions works, and drops XCTest dependency