XCode 11 SPM support

[urosk]

Updated package definition and project structure to allow direct importing via XCode 11 SPM.

• Package manifest created with Swift Tools 5.1
• Moved files around to comply with default folder structure for SPM

[hkellaway]

hi @urosk ! thank you so much for contributing

what's a good way to verify this? i'm not super familiar with SPM

[urosk]

Hi!
Test this by:
1.) Open XCode 11
2.) Open the project file and click the project (not target)
3.) Click packages tab
4.) Click + to add a package
5.) Pick Gloss (note: it has to be favorited on the GitHub account you use in XCode)
6.) Enter "XCode_11_SPM" in the branch field

The package should be correctly resolved, and added to XCode. Importing Gloss should work. Tests should run.

Keep in mind though, that I totally rearranged the files in folders. I'm not sure if any other supported package managers expect a fixed folder structure. If yes, we could also try to preserve the old structure by specifying a custom SPM path.

[hkellaway]

this is awesome - thanks for doing that (and for teaching me a bit about Swift PM!)

i'll work on a 3.1.0 release this week - til then, you can point to develop

[hkellaway]

Gloss 3.1.0 has been released with support for SPM! 🎉