Mac catalyst support

[DanBurkhardt]

Commit Msgs:
Enabled markdownview for macCatalyst apps, build settings require iOS 13 + OS X 10.15, symantec version increase for non-backwards compatibility, entitlements modified for RW access to UserDefaults in catalyst, layout contrainsts fixed for running in catalyst env, podspec version increase, summary modified for catalyst compatibility, podfile enables submodules, modular headers, incremental builds, inhibits warnings in podfile.

Testing:

• both the example and framework updates are fully tested for both iOS and macCatalyst
• Run your own tests by running the example project to iOS sim, and then run it locally to your Mac

Notes :

• Catalyst apps are still early days compared to iOS, but there are a lot of issues with Cocoapods due to lack of cocoa pod support. Therefore, the incrementalized installation settings, and submodule settings in the Podfile are required.
• If you don't use incremental / submodules, you cannot sign the application, which is an unhandled issue when the .xcworkspace is generated by cocoapods for catalyst apps.
• Also, had to change the bundle / team ID to run and test locally, obv need to change that before update to Cocoapods

[DanBurkhardt]

Hey @keitaoouchi & @stevearm, looking for a possible review! Lmk what you think.

[DanBurkhardt]

@keitaoouchi saw you had the latest commit, can you please review?