Add LANGUAGE extensions for inferred signatures.

Some of the inferred signatures required LANGUAGE extensions that
were not enabled. Since now GHC checks that we have to explicitly
list required extensions.
Backport .travis.yml from master branch
Update vector.cabal and bump version to 0.10.9.2

This backports some changes from the vector.cabal file in the master
branch, including the external changelog and more importantly a change
of the maintainer-field.
Backport OverloadedLists support from master
Bump version to 0.10.9.3
Perform minor version bump to rectify PVP violation

The patch-level bump in 60cbe2c6ec2796da4d187caf018ed24d697f1f09 didn't suffice
to conform to the PVP, as in 3cbb0ec457358bc55ee0a2408bb60d45f4f01acf a new instance
was defined, therefore at least a minor version bump would have been needed.

By uploading a 0.10.10.0 release, and declaring the 0.10.9.3 release a "non-preferred"
release, everything should be fine again.
Backported (manually) IsList implementation for boxed Vector
Releasing 0.10.11 for fixed OverloadedLists support
Export Primitive Vector's constructor

- Document briefly Vector's and MVector's fields
Prepare 0.10.12.0 release.