Use "dub.json" instead of "package.json" in documentation

fix issue with missing dub.selections.json ...

- the dub.selections.json file was no longer generated
  for packages without dependencies

- this lead to an error when checking for the timestamp
  of the selections file later on

- an alternative fix would be to ignore the timestamp
  when no selections file exists

Removed 'Wide' from PlacementLocation member names.

Merge branch 'upstreammaster' ...

Conflicts:
	source/dub/project.d

Implement support for $ROOT_PACKAGE_DIR and $<PACK_NAME>_PACKAGE_DIR variables. Fixes #260. ...

PACK_NAME must be all uppercase and dashes (-) must be replaced by underscores (_).

Added support for fetching to any location, now need to add support for finding packages in other locations.

*Rally* only overwrite dub.selections.json if necessary.

Rename m_selectedVersions -> m_selections.

Only overwrite dub.selections.json if there are actual changes.

For "dub run", change the CWD only if non-empty. Fixes #272.

Fix path based dependencies. See #282 and #253.

Detect dependency cycles after version resolution and before configuration resolution. Fixes #280.

Fix building sub packages that depend on their own parent package.

Fix usage of the selections file (was completely ignored) and improve diagnostic output.

Avoid internal exception when loading version selections.

Rename UpdateOptions->UpgradeOptions and move it to dub.dub.

Properly support path based version selections.

Fix validating the configuration graph. ...

getTopologicalPackageList(), which was used before, could yield a different set of packages.

Resolve sub packages of the root package directly instead of using the package manager. Fixes #287.

Fix null pointer dereference in Project.this() when no package was found. Fixes #286.

Fix compilation on DMD 2.064.

Fix path based dependencies to be ignored for version selections.

Implement user/system wide overriding of certain package version ranges. ...

What is still missing is a command line interface for conveniently setting the overrides.

Only validate (and output warnings) the root package once.

Improve the warning message for branch based dependencies.

Add a warning message for packages that use branch based dependencies.

Rename Project.mainPackage to rootPackage. ...

Root package better describes the package's role of the root of the dependency hierarchy.

Implement a new dependency resolution algorithm with support for selections. ...

The new algorithm is completely rewritten to be able to find any valid combination of dependencies/versions. The old one could error out in cases where a valid dependency tree could have been built. Now the current selections are also taken into account when invoking without UpdateOptions.upgrade.

Some side changes:
 - Comparing branch versions is allowed now to enable sorting the full set of versions of a package
 - DependencyGraph and RequestedDependency have been removed

Rename fields in Project and load the root package only once.

correct imports