Add initial assert helpers

Closes #110
Remove trailing whitespace from the Python
Fix whitespace for async test detection

Presumably since Python is whitespace-sensitive, this is actually quite important?
Example of using assert.js
Merge pull request #123 from domenic/whitespace-fixes

Whitespace fixes
add "assert.js" to python, website runners too
Merge pull request #124 from domenic/asserts

Initial assert helpers
Merge pull request #127 from smikes/asserts

add "assert.js" to python, website runners too
Add assert.throws

Closes #57.
Add an example of using assert.throws
Merge pull request #131 from domenic/assert-throws

Add assert.throws
Move S9.9_A1/2 to proper locations

The with statement tests were novel, but the tests for
property accessors throwing errors for undefined & null
were duplicates with S11.2.1_A3_T4/5 respectively.
Reorganize ./test