strip trailing spaces
the option has been set in find_magic()
no need to force()
more cosmetic changes, and renamed find_Magic() to find_magic()
convert should not be NULL
use shQuote() only when it is really needed in command line
add @mingsnu as a contributor
news about #35
bump version
Revert "use 'shell' instead of 'system' on windows"

This reverts commit 4cfd280d75a9e1e9a653ad2630478032e475bc0f.
actually cmd != 0 means failure