Clean up doc directory

- removed NWPT source code (now in papers companion repo)
- removed stale slides
- moved HIPERFIT slide set up
instruction fix
new header stuff for pretty printing and hiding
playground
cleanup
fix definition of specialisation
advance
monadic interface
on request
change
fixes
fixes
horizon defined as in the paper
add first draft of technical report
change semantic representation of cash-flows

The semantic representation of cash-flows is "anti-symmetric" in the
sense that at any time t for which C[|c|]rho (t) is defined, the
semantics must satisfy that

C[|c|]rho (t) (p1,p2,c) = C[|c|]rho (t) (p2,p1,c)
Merge branch 'master' into extrinsic

Conflicts:
	Coq/Denotational.v
	Coq/Extraction/Header.hs
	Coq/Horizon.v
	Coq/Syntax.v