Customising IB mask properties

[tbaranes]

Here a first version of mask customisation from IB following the related threads. Should closed #8 #50 #76

The following implementation has been done for:

• StarMask, IB usage: Star(6), Star(12)...
• WaveMask, IB usage: Wave(up,50,100)

If one parameters is missing, or miswrite, we will fall back to the basic implementation with default values.
I also allowed some miswrite errors: Star(6 is accepted, as well as Wave(up, 50, 100)

Finally, I didn't implement the swifty enum. I concluded that we will still need a string enum in order to avoid hard coding strings or multiple constants for each mask. So, even if it's more swifty to have the following one, it will just create duplicates code.

public enum Mask {
    case Circle()
    case Star(branches: Int)
    case Wave(up: Bool, width: Int, offset: Int)
}

Missing:

• README update: don't really know how to explain this feature... so I prefer let you handle this (if you don't mind)

I'm waiting your feedbacks on that :)

[JakeLin]

@tbaranes , thanks for the PR, I found out it didn't work before because MaskType(rawValue: unwrappedMaskType) will return nil if we specify the parameter like Star(6), I have fixed it by adding additional check like

if unwrappedMaskType.hasPrefix(MaskType.Star.rawValue) {
        maskStarFromString(unwrappedMaskType)
      }

I have tested them, please have a look at my changes. Will update README.md later once we get that in master.

[tbaranes]

Thanks for the fix Jake, I miss that point after refactoring the PR... my bad.
I'm gonna merge the PR once travis has finished its builds.