Extract SigmaParser and deps into a new module

[darkdrag00nv2]

Ground work for #851

Extracted SigmaParser and its dependencies to a new module named parsers and added support for cross-compilation on it.

This was needed because in order to decode a ContractTemplate for EIP-5, we need to decode the SType from the JSON. Support for doing that is available in SigmaParser which needs to be available from the sdk module. This helps avoid the sdk module depending on the sc module.

[darkdrag00nv2]

@aslesarenko This mostly works except one problem. The SigmaParserTest which I've moved to the parsers module has some test case that use the SigmaCompiler. See here. The parsers module can't depend on the sc module as the later already depends on the former.

I can see two solutions:

1. Keep SigmaParserTest inside the sc module itself. Probably not ideal
2. Move the test cases that do not need the SigmaCompiler to the parsers module and move the remaining to SigmaCompilerTest

Thoughts?

[aslesarenko]

Move the test cases that do not need the SigmaCompiler to the parsers module and move the remaining to SigmaCompilerTest

@darkdrag00nv2 This sounds good.

[darkdrag00nv2]

Ran the tests using +test and they all pass.

[darkdrag00nv2]

+test still works.