can parse and pretty-print linear implication formulas

uses lollipop symbol '-o' for linear implication, as in A -o B meaning A implies linearly B.
only handles parsing/pp as resolution requires a little more machinery...
fix documentation generation for haddock

introduces a library section in cabal and make hslogic executable depends on it
documentation can be generated by 'cabal haddock'
note that mixing regular comments with doctest is not supported...
introduce explicit Context type to maintain list of goals
introduce linear conjunction (tensor product) formula

linear queries are resolved as though the context was linear and intuitionistic queries
as though the context (eg. set of clauses) was intuitionistic