Problem: It happens that "go to definition" fails with lambda
parameters meaning that we do not create proper AST for it.
Also we need to restructure grammar so that we can support it in
the future.
Solution: Restructure grammar to use "param_decl" and ensure that
we use proper fields for parser resolution.
Problem: With generated ReasonLIGO grammar we need to develop its
parser as well. With it we also need to restructure AST a bit
and add expressions that are used for ReasonLIGO specifically.
Solution: Add ReasonLIGO parser and some dummy examples of its
usage, adapt AST to it, rename LIGO to AST.
