REIMPLEMENTATION grammata 0.2.0.15

for now finished the virtual machine. Still stuff to be done; see past commit messages.
    Grammata.Machine

implemented abstract syntax tree of arithmetical expressions for the grammata language.
    Grammata.Language.AST.Expression

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On branch dev
Changes to be committed:

    modified:   grammata.cabal
    new file:   src/Grammata/Language/AST/Expression.hs
    modified:   src/Grammata/Machine.hs
    modified:   src/Grammata/Machine/Core.hs
    modified:   src/Grammata/Machine/Core/Imperative.hs
    modified:   src/Grammata/Machine/Core/Logical.hs