move code to manage twig template functions into separate namespace
allow redefining template functions. wrap exceptions in FunctionException
get rid of debug println
add support for template function aliases
add standard functions (those not already provided by jtwig)
pprint isn't really a 'core' function i guess, so we should have a :use

tests failed to run, complaining about pprint being undefined until this
was added anyway
typo
standard function now defined in a map which can be easily reloaded
add no-alias arg overload for add-function!. update some doc comments
move template function tests into a separate namespace. add std fn tests
add more standard function tests
update version