chore: add license to opam files

many bugfixes

chore: fix constraints in opam

changed defaults

prepare for 1.6

chore: fix opam file wrt missing test-dep for logtk, jobs, conflicts

Merge branch 'master' into stable for 1.5

Prepare for 1.4

Merge branch 'master' into stable, prepare for 1.3

Merge branch 'master' into stable for 1.2