Undocumented SAWScript syntax

[nano-o]

The following SAWScript syntax elements are undocumented or the documentation is hard to find:

• if-then-else
• syntax for accessing elements of tuples, e.g. .1 and .2
• let ... in
• syntax for defining recursive functions
• syntax for instantiating type variables

Those might seem evident but it can cause a little frustration for a beginner.

[brianhuffman]

I will make a pass over the SAW manual and tutorial in time for the next release. We should take particular care to explain the relationship between SAW and Cryptol syntax in the documentation.