Internal rewrite of dependencies:

- If applicable, PackageManager subclasses should represent high level tools like Yum and Zypper, not RPM
- We will utilize this when writing managers for different systems
Add PacmanPackageManager (to be tested)
Remove extraneous is_installed method from package managers, we are ok with just works()
If Python is not compiled properly with sysinfo, get distro name from /etc/os-release
Fix PacmanPackageManager

- invoke installation with --noconfirm so that pacman doesn't freeze waiting for input
- don't fail if package is not present, just return false in is_pkg_installed
- fix typo in works()
Note that we can now install dependencies on Arch
TestCommand
Part of tests for command_runners + AskCommandRunner.format_args throws exception on bad Command format
Fixed AskCommandRunner to work with old pytest
Add a --no-cache option
Allow specifying additional data dirs by using environment variable DEVASSISTANT_PATH
Update and improve excepthook after it was broken by refactoring functionality into devassistant.lang
More tests for command_runners
Moved GitHubAuth to new remote_auth module
Update manpage for da with latest improvements
Update changelog with latest improvements
Add explicit info about which version the documentation applies to.
Don't fail with traceback if no superassistant is found
Remember sourcefiles in kwargs rather than in argument passed to run_section

- it's more flexible and usable also in dependencies
- it allows command runners to access this value, possibly adding it to error messages.
Revert "closes #114 Introduced list, delete and save projects into cache handled by DevAssistant"

This reverts commit 16655f366c07965b5abb24387bd48674b49f09bf, which
has to be rethought and implemented in a better way.