Created CONTRIBUTING documentation and udpated README
Merge pull request #18 from dotta/feature/contributing-documentation

Created CONTRIBUTING documentation and udpated README
Added build profile for Scala IDE for Eclipse Juno

* Updated tycho version to 0.16.0.
* New ``juno`` profile for building the plug-in for
  the Scala IDE for Eclipse Juno (default values are
  for building the nightly Scala IDE for Eclipse Indigo)
* Updated default scala.version to:
    * 2.10.2-SNAPSHOT when building against the Scala IDE 4.0.x nightly.
    * 2.10.1 when building against the Scala IDE 3.0.
Merge pull request #20 from scala-ide/issue/fix-pr-validator

Added build profile for Scala IDE for Eclipse Juno
Stores occurrences of methods in Lucene

The plugin now keeps an Index (using Lucene) of all the places
methods are mentioned in the code-base. A separate Lucene index
is created on disk for each project.

The initial indices will be created upon start-up if no index
exists already. It will index the entire workspace and traverse
the parse-tree of all Scala sources.

For each project in the workspace we create a background job that
continuously update the index and re-index files that have changed.

There are two separate tests: OccurrenceCollectorTest contains test
that make sure we record the correct information from the parse trees
and IndexTest that makes sure the occurrence information can be stored
and retrieved from Lucene.

Fix #1001602
Merge pull request #19 from mads379/indexing-methods-using-lucene-API-1001602

Stores occurrences of methods in Lucene
Use project relative paths in index

We now rely on a combination of project name and a project
relative path to keep track of files in the Index.

Fix #1001632
Merge pull request #21 from mads379/1001632-use-workspace-relative-paths

Use project relative paths in index
Improved tree traversal

This fixes four issues

- The code used super.traverse to recurse the trees. This was wrong
  as it would skip one 'layer' of nodes.
- Traverse the argument list of DefDef's
- Traverse annotations on DefDef's
- Store occurrences in ValDefs

So it turned out that the failure that was seen with the string
interpolation test had nothing to do with string interpolation.

Originally it only found one occurrence of `x` in the following
example.

  def foo(x: String) = s"Hi there, ${x}"

I assumed that the `x` that was missing was the one inside of the
string interpolation, but actually it was the argument. Ups.

Fix #1001621
Merge pull request #23 from mads379/1001621-record-occurrences-in-string-interpolation

1001621 Improved tree traversal