Makes search case insensitive.
Implemented tag querying for git. Ref #18.
Search will now continue even if packages are found based on tag name.
Merge branch 'pr_case_insensitive_search' of https://github.com/gradha/babel into gradha-pr_case_insensitive_search

Conflicts:
	babel.nim
Remote tag querying for search and list.
Version querying is now disabled by default.
Updated readme.
VCS commit hash, branch or tag can now be specified when installing
packages.
Updated readme to mention specific commit installation.
List command supports --ver now.
Versions in .babel files are now verified.
Replaced quit() in packageinfo with an exception.
A URL can now be specified for installation.
Documented installation by URL.
Added a more descriptive error when trying to install a version of a
package which does not exist.
Better download dir names for URL dependencies.
Extra checks for unsatisfiable dependencies.

Specifically this refers to the problem with babel-test/packagebin.
PackageBin ends up depending on two different versions of PackageA (0.2
and 0.5). This however cannot be built because the Nimrod compiler can
only use one of these packages.
Fixes #21
Fixes problems caused by "" being present in the version list.

Specifically, not being able to install nim-vorbis.
Git checkout is now forced.

This has been done to fix an issue on Windows. The issue is that Git
may think that line endings have been changed straight after a clone
and thus disallow the checkout because "local changes are present".