Add a --raw option

This option is used to load a view from any --pretty=raw output.

This allows you to run:

    git log --pretty=raw | ./tig --raw
    git reflog --pretty=raw | ./tig --raw
    git stash list --pretty=raw | ./tig --raw
    git rev-list jonas/code-split --pretty=raw | ./tig --raw
    git whatchanged --pretty=raw | ./tig --raw
    ...

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>