replace all imports by relative imports to avoid conflicts

[timotheecour]

replace all imports by relative imports to avoid conflicts, eg in case multiple versions of wrappers are installed

proposal 1

robust but annoying as you need to compute relative paths for each import

import wrapperspkg/foo
=>
import "../../" / wrapperspkg/foo

proposal 2

implement support in Nim for:

import wrapperspkg/foo
=>
import root/wrapperspkg/foo # root of nimble pkg containing this file

which extends the existing special syntax import pkg/foo/bar

alternative names:
tpkg (ie: this pkg)