Expose --target-dir <dir>

[ralpha]

Geiger does not seem to re-export --target-dir <dir> flag and it is thus rebuilding my project when I switch between different build steps.

This might be related to #16, #69 and #95

[anderejd]

Thanks for opening the issue.

There's another thing that needs to change to avoid rebuilds, cargo-geiger currently performs a clean build every time to make sure the compiler output is related to the latest cargo-geiger execution. Let's wait for #16 to be completed.

[pinkforest]

Cargo decoupling is on it's way for the next major so we can relay cargo flags as-is.