Split the Learn L4 into two paths

Split the Learn L4 section into two paths:

1. input (how to write L4)
2. output (explanations of transpilation targets)

Add note re formweaver and clarify webform docs a bit

1. Add quick note re form weaver in webform.rst
2. Clarify what the most important two things for understanding how to make a web form are

23.12.04: Merge pull request #25 from smucclaw/cleanup-tle

t-le: comment out the TODOs in transpilers-logical-english.rst; add a few quick explanations / clarifications

23.08.16

Merge pull request #14 from smucclaw/relpred-docs

docs for semantics and relationalpredicates