Mode : remove the `new Mode.forFile` factory

this was a subjective, incomplete, and static mapping and it is
preferable to delegate such logic to an application which can map
dynamically based on context and/or user preferences.
EditSession : split `annotations` into `getAnnotations` and `setAnnotations`
`setAnnotations` methods

this matches `ace.js` and helps to clarify their separate behavior.
EditSession : replace the `breakpoints` getter with the `getBreakpoints` method
Mode : reinstate the `Mode.forFile` factory

it is now user-configurable
Merge pull request #26 from rmsmith/v0.2.0_breaking_changes

V0.2.0 breaking changes