operator+ concatenates two vectors.
Computations added.
Added show implementations for computations.
Minor changes.
Computations' constructors added.
test-lang updated.
Using operator+ to concatenate vectors...
serialize functions added for computations.
Minor changes
test-lang updated.
pfq-lang updated.
pfq-default and related test added.

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CMakeList updated.
Using std::bind simplifies the implementations of polymorphic functors.
Makefile updated.