Add support for DUBPATH and "add-path" + change the default installation location to the DUB user path. Fixes #64. ...

This change allows to specify a number of directories in addition to the system and user DUB package directories to search for local packages.

Full list of changes:

 - Add support for the DUBPATH environment variable (a (semi-)colon separated list of paths)
 - Add support for "dub add-path" and "dub remove-path" to add static search paths
 - The branch of local packages with no "version" field in their package.json is now inferred using "git rev-parse"
 - The structure of the user/system package directories is changed from "packages/<packname>/<packver>" to "packages/<packname>-<packver>"
 - There is no project local package directory (".dub/packages") anymore - packages are instead installed to the user package directory by default
 - Upgrading and uninstallation is partially broken in this commit - will be fixed later

Implement a first version of "dub describe".

Add warning for package names with upper case letters, but handle them gracefully.

VisualD generator: Fix x64 builds and avoid building header only dependencies.

Compile fix for DMD 2.053 beta.

Updating optional dependencies themselves, when they are available.

Fixing issues in getTopologicalPackageList and getPackageConfigs because of added "optional" flag for Dependencies.

Package updating could work with optional dependencies.

Fix recursive determination of sub configurations. ...

See also #65.

Fix build settings for dependencies in the VisualD generator. ...

Paths were relative to the dependency package path rather than the main package path where the project file is generated. Also, versions and other build settings were not only inherited from dependency to dependee, but also the other way around.

Move all source files outside of "dub" to "dub/internal".

Implemented "buildRequirements" as a way to avoid certain compiler settings for specific code bases. ...

See also #61.

Support "-ddoxFilterArgs" field to control how --build=ddox filters documentation entities.

Improve output of the dflags warning message. Fixes #54.

Always upgrade branch based dependencies. Fixes #55.

Fix building in directory without package.json.

Fixed recursive configuration deduction and improved error messages for invalid package.json files.

Prepare for multiple registry support, update stdx.process and make env vars available to custom commands. ...

See also #22.

Added a "subConfigurations" field and implemented proper configuration selection for dependencies.

Added "targetName" and "targetPath" build settings and some fixes. ...

Other changes:
 - Made the comparison for "excludedSourceFiles" path format agnostic
 - Fixed the output directory for the VisualD generator
 - Removed the "binaryPath" global setting (which was undocumented up to now)

See also #26 and #29.

"sourcePaths" is now a build setting instead of a global field.

Improved configuration selection for dependencies. ...

Still missing a way to select a specific configuration for each dependency.

Change the way configurations are specified. ...

Configurations are now given as a list instead of a map and the defaultConfiguration field was removed. Instead, the first configuration that matches the target type and platform is chosen.

The internal package representation is now JSON agnostic + streamlined configuration and dependency handling. ...

Still missing for the new configuration handling:
 - A way to select which configuration to use for a dependency (instead of the default "library")
 - New method to define a default configuration per platform and mode (application/library)

Fixed the order of build flags for the dependency tree (dependencies must go first).

Source files are now collected at a central place instead of in every generator. ...

Package.getBuildSetting() now determines all source folders and recursively collects all source files there.

Implemented pre/post commands and --build=ddox + support "sourceFiles". ...

Other fixes:
 - fixed class Dub to work with other path than cwd
 - "files" has been deprecated in favor of "sourceFiles"
 - --build=docs also works now
 - Changed the way build flags are parsed (instead of checking every possible field for existence, all fields are iterated and their name is matched)

When the user calls install from the command line, a dependency will be added to the project's package.json. However, this will reformat that file. Should now perform more like user expectations mentioned in #12.

Fixed naming convention for enum InstallLocation and avoid reinstalling packages that are already up to date.

Fixed "dub upgrade" when a package is stalled user or system wide.