Investigate support for interpreting templates

[afscrome]

Currently we compile the templates This has a startup cost, which then leads to further startup costs on the first execution whilst the template is JIT compiled. We should look at whether we can interpret these templates to speed this up. This could be done either using the DLR scripting bits as used by IronPython. Alternatively depending on dotnet/corefx#3244 this support may be built in.

A hybrid aproach could also be adopted to compromise on startup time vs raw performance - interpret a template the first X executions to optimise for startup speed. After X executions, compile in the background then swap to use the compiled template. I believe this is alreadyd one in the DLR scripting bits, but would need to check.