Modified MGLAttributedExpression object to support NSExpressions as formatting attributes only. This aligns with GL and Android implementation and specification.
Modified the documentation accordingly, and changed MGLFontSizeAttribute to MGLFontScaleAttribute to clarify the true function of the formatting parameter.
Added the possibility of overriding paint properties inside the format expression.
Added an example of how to create an MGLAttributedExpression object and documented the attributes keys and value types.
Fixed a bug that ignored the font names.
Added the ios/macos format expression bindings.
The equivalent is mgl_attributed: or mgl_attributed({}) when making an expression using the expressionForFormat selector.
A new constructor called mgl_expressionForAttributedExpressions:(NSArray<NSExpression*>*)attributedExpressions was added to NSExpression+MGLAdditions category.
Updated the symbol style layer text test to use the bindings.
Updated the Predicates and Expressions.md and For Style Authors.md.ejs template with the bindings.
