Merge branch 'release/v0.0.2' into develop
include xclip in requirements

also list arch install command,
although arch doesn't work because tempfile is missing
(mktemp will work instead).
use mktemp as a substitute for tempfile
add note about missing `scrot -u` on some systems
clean code, improve error messages

condensed some simple `if else` to `&& ||` one-liners.

specific errors reported for scrot, curl, or imgur failures.
release v0.0.3

support systems without `tempfile` (e.g. Arch)

improve error reporting
Merge branch 'release/v0.0.3'