...<command> argument (but still resolve tilde).
This makes it easier to write sh -c '' constructs without turning labwc
into a shell parser in order to expand environment variables, whilst
respecting single quotes and escaped characters as well as ignoring
subshells syntax like $(foo) and backticks.
Also, fix bug where buffer length+alloc get out-of-sync
Expanding shell variables, including tilde, enables the following type
of keybind:
<keyboard>
<keybind key="XF86AudioMute">
<action name="Execute">
<command>bash ~/mute-script.sh</command>
</action>
</keybind>
</keyboard>
Fixes issue #32
