dest-dir should be relative to the current dir and not to the book root

[konstin]

mdbook build -d ./my_out_dir guide generates the book in guide/my_out_dir and not in the expected my_out_dir. mdbook build -d /tmp/out_dir guide otherwise doesn't build the book in guide/tmp/out_dir, but in /tmp/out_dir.

This can lead to extremely confusing situation, e.g. mdbook build -d ./out_dir guide and mdbook build -d $(pwd)/out_dir guide build to different locations.

[mattico]

Fixing this would be a (minor) breaking change -- it could break people's CI. I forgot to change this for 0.2, but hopefully adding it to a milestone will help me remember.

[gnzlbg]

+1. I find this extremely confusing.

[gustavovalverde]

Old one, but definitely very confusing.