Add support for the short-circuit logical operators && and ||.
Add support for cascades.

Much like declarations, if a cascade section immediately to the right
contains an await, all the accumulated cascades must be residualized.
Merge pull request #29 from kmillikin/short-circuit

Short circuit
Merge pull request #31 from kmillikin/cascades

Cascades
Support postfix expression.

Also, fix a bug in variable declarations.  If there was no
keyword (i.e., there was a type but no `var`, `final`, or `const`)
then the keyword and type were both omitted.  This is fixed to emit
`var` as a workaround, though the type should be emitted instead.
Merge remote-tracking branch 'upstream/master'
Merge pull request #34 from kmillikin/cascades

Support postfix expression.
Merge remote-tracking branch 'upstream/master'