Macros support.

Macro functionality is done through Annotations. When clicking on
expand macro annotation macro expands into the source code, annotation
to collapse is added to expanded region. When clicking on collapse
macro annotation macro is erased with expandee.

When triggering save command performSave function of
ScalaSourceFileEditor is called. Before actual save every macro is
erased with its expandee, so that source file doesn't contain any
macro applications.

Through createLineNumberRulerColumn function line number
column for custom line numbering is integrated. It internally stores regions, where
macros are and change line numbers where neccesary.

Macros can be turned off by clicking on the Enable macro icon,
M1+M2+M(Ctrl-Shift-M) shortcut or through preference page.
Don't use inline comments, they are evil. Use Scaladoc and move out complex expressions to methods. You can never know how much a reader of your code knows about the API. Essential things need to be commented therefore.

```scala
def treeAttachment[A]: Option[A] =
  t.attachments.get[A]

/**
 * This is new API? The API is available when ... The Map contains ... and ....
 */
val ScalaMetaProvider = treeAttachment[jave.util.HashMap[String, Any]]

/**
 * This is old API? Fallback API when ScalaMeta is not available. The MEA contains the necessary values ... and ...
 */
val ScalacProvider = treeAttachment[compiler.analyzer.MacroExpansionAttachment]

/**
 * Conforming to ScalaMeta API ... under the "expansionString" key.
 */
def ScalaMetaHandler(att: ...) = ...

/**
 * see [[compiler.analyzer.MacroExpansionAttachment]]
 */
def ScalacHandler(att: ...) = ...

// well, andThen doesn't exist for Option, but you get the idea.
(ScalaMetaProvider andThen ScalaMetaHandler) orElse (ScalacProvider andThen ScalacHandler)
```