myrialang: remove trivial sequence operators with only one child

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
myrialang: compile_to_json handle single operators

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
Merge pull request #96 from uwescience/dhalperi-optimize-myrial

Dhalperi make single-line Myrial programs executable