Fix misleading name.

This variable contains the name of the executable which outputs JSON data from Javascript,
but the old name makes one think it contains the name of the file with JSON data.
Rename Ljs_desugar.desugar to Ljs_desugar.parse_and_desugar (misleading name).
Merge pull request #32 from ProgVal/fix-misleading-names

Fix misleading names