[#104] Show sample values in autodoc

Description

Problem: Documentation produced by our autodoc engine shows argument type of each entrypoint which is good, but people who use vanilla Michelson may have difficulties constructing a value of that type. In order to make their life a bit easier we can provide some sample value of that type.

Solution: Generate sample values from entrypoint type. Add a way to modify those same values value with desire values.

Related issue(s)

Resolves #104 (closed)

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