Add desugaring of `foward`

[JSAbrahams]

Relevant issues

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Summary

We have the forward keyword, similar to Perl. This allows us to easily forward methods of the contained object (remember, we use composition, not inheritance). This is only a partial implementation however, we still have no way of checking what arguments the method of the contained object requires. Once we have a way of building a context which contains information about each identifier's type and the accompanying methods we can look up which arguments are required for a forward.

In short, the following:

# a is a method which takes no arguments, b takes two arguments
def private my_class <- MyClass() forward a, b

Is essentially desugared to the following:

_my_class = MyClass()
def a(self): self.my_class.a()
def b(self, arg1, arg2): self.my_class.b(arg1, arg2)

Although currently, due to not knowing any information about methods a and b, it is for now (incorrectly) desugared to:

_my_class = MyClass()
def a(self): self.my_class.a()
def b(self): self.my_class.b()

Added Tests

Test to check that desugaring of a foward produces a block with:

• The original variable definition
• A method for each single forward

Additional Context

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[codecov[bot]]

Codecov Report

Merging #74 into master will increase coverage by 0.31%. The diff coverage is 87.12%.

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
+ Coverage    80.2%   80.52%   +0.31%     
==========================================
  Files          60       60              
  Lines        3925     3974      +49     
==========================================
+ Hits         3148     3200      +52     
+ Misses        777      774       -3

Impacted Files	Coverage Δ
tests/output/syntax.rs	46.66% <ø> (+2.91%)	:arrow_up:
src/parser/ast.rs	23.94% <100%> (-0.71%)	:arrow_down:
tests/parser/valid/definition.rs	90.35% <100%> (+0.8%)	:arrow_up:
src/parser/definition.rs	82.43% <100%> (ø)	:arrow_up:
tests/desugar/definition.rs	86.89% <82.92%> (-2.11%)	:arrow_down:
src/desugar/definition.rs	85% <86.36%> (+0.9%)	:arrow_up:
src/core/construct.rs	32.98% <0%> (+12.37%)	:arrow_up:

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