Add sy#util#run_in_dir to run system() within a specific directory

Signed-off-by: James McCoy <vega.james@gmail.com>
Replace all uses of "cd … && do_something" with sy#util#run_in_dir

Signed-off-by: James McCoy <vega.james@gmail.com>
Merge branch 'UNC-paths'

Closes #114