Add support for custom location for vendor directory

Thanks for the PR!

Corrected usage for --cacheDirectory & --forceRefresh options

Fixed documentation in help & README for how to use the --cacheDirectory & --forceRefresh command line options.

When using the install command, the --cacheDirectory flag should be used after install, but before the specific installer arguments.

For example, the syntax to use npm-cache where you want to specify --cacheDirectory & npm install with the --force option is:
npm-cache install --cacheDirectory <my/custom/cache/dir> install npm --force

Namespace cache by installer & installer version

Cached files will now be located in <cache_directory>/<installer name>/<md5_config.tar.gz> instead of just <cache_directory/<md5_config.tar.gz>. This will allow you to work with different versions of installers and still being able to trust npm-cache

Example new directory structure:

~/.package_cache/bower/1.4.1
~/.package_cache/bower/1.4.1/d41929551e416aa2ffb36c462afe3d34.tar.gz
~/.package_cache/composer/1.0.0-alpha9
~/.package_cache/composer/1.0.0-alpha9/c1742a40235c0671609fe5f87d6f7e4a.tar.gz
~/.package_cache/npm/1.4.28
~/.package_cache/npm/1.4.28/704d24c9f8406b7965a190bd0c664186.tar.gz

Clear install directory before extracting dependencies -- Fixes issue #5

0.3.1

bump version to 0.3.1

Added npm-shrinkwrap.json support

npm-cache now checks for npm-shrinkwrap.json instead of package.json if it exists.

Small bugfix for version option

0.2.1

bumping version number for bug fix

Added ability to specify custom package manager options

Added ability to specify custom package manager options. For example, if you need to install bower components with the --allow-root option, and composer with the --prefer-source option, you can do the following:

npm-cache install bower --allow-root composer --prefer-source

Specify the package manager name followed by any custom options. This release does not break previous functionality

Bug fixes plus use async more correctly

0.1.0

update das package version

Added version number option

Specifying --version of -v displays version number

Refactors, clean-up, and new options

• Remove unnecessary init() function
• Replace JS inheritance in cache dependency manager with config objects
• Replace yargs with nomnom for better CLI command routing
• Remove checked-in composer.phar (use user's installed composer)
• Use async library to load dependency managers asynchronously
• Added clean command
• Added forceRefresh command