freeze coercions

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branch : feature/freezy-coercion
allow libraries to contain floating coercion objects

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branch : feature/coercion-libs
allow coercions to be added together

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branch : feature/coercion-libs
allow coercions to be added to type constraints

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branch : feature/coercion-libs
docs

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branch : feature/coercion-libs
merge feature/coercion-libs: allows coercions to be frozen; allows standalone coercions to be added to type libraries; coercions override plus