Better emulation of C in executor wrt file handles

Now, we return a null pointer on failure to open a file, and we allow
isNull to check handles as well as pointers. For handles, it returns true.
Minor tweak to pretty-printing lambda

Indent the body of the lambda slightly
Use pretty-printer to show the result of :x
Decorate type provider errors with source location
Test updates for executor and type provider update
Whitespace cleanup
Make IdeSlave mode follow :consolewidth commands
javascript: move Con and Cont into codegen
javascript: rename JSOp into JSBinOp
javascript: added JSPreOp and JSPostOp
javascript: unfoldLookupTable
javascript: JSWhile
javascript: moved EVALTC and APPLYTC into codegen
javascript: make unfoldLookupTable work
Add a template for bijections to/from primitives

RE #833
Add iso between String and List Char
Merge pull request #842 from Melvar/ideslave-consolewidth

Make IdeSlave mode follow :consolewidth commands
Merge pull request #843 from raichoo/javascript

Javascript
Add js tests to travis script
Annotate and colour pairs and () properly

Now, the delaborator remembers if a particular unit or pair is the type
or the constructor, and colours them accordingly.