Refactor the compiler options.

Define default options in class constructors.
Export ToAmdCompiler and ToCommonJSCompiler with corresponding defaults.
Remove options unique to api (not on command line).
Add option moduleName (default true) to support commonjs w/o __moduleName.
Option moduleName takes string, empty string for no __moduleName, or '+' for
  resolve filename.

Review URL: https://github.com/google/traceur-compiler/pull/1079

Closes #1079.
Export default declarations should introduce a binding

`export default class C {}` should introduce a binding for C in
the current scope.

Fixes #1062