Implement support for SFSymbol 6.0

Update README.md

Merge pull request #28 from adamwulf/fix/missing-horizontal-key

Adding missing key.horizontal and key.horizontal.fill

Gardening, add convenience init for supporting variable values and te…

…st fixes.

Merge pull request #25 from Nirma/fix/lint

Linting the project

Merge pull request #18 from vincentneo/fix/macOSAvailability

macOS 11 @available for initializers

Update README.md

Update SFSymbol.podspec

Update SFSymbol.podspec

Update SFSymbol.podspec