Expose compiler, use let instead of const, map updates

[extremeheat]

• Exposes CompiledProtodef for easier debugging/using already compiled js
• use let instead of const for containers, allows for variables to be modified after (used here)
• mapper type now returns the number if mapping fails (avoids needing to map lots of unknown values)
• sanitizeMappings now converts strings to numbers/booleans to match the logic in switch statements https://github.com/ProtoDef-io/node-protodef/blob/master/src/datatypes/compiler-conditional.js#L13 , previously mapping numbers would work because of type coercion: switch ("355") { case 355: ... } == "355" == 355 however the same won't work for booleans : ('true' == true) returns false.

[rom1504]

Can you update the doc ?

[rom1504]

Add what you exposed there https://github.com/ProtoDef-io/node-protodef/blob/master/doc/api.md#protodefcompiler