POSIX permission operations

[eed3si9n]

This adds wrapper methods and functions around NIO's POSIX operations.
The implementation is heavily based on @pathikrit's better-files library, but I've made some minor changes.

• sbt IO supports 2.10 - 2.13.
• I've added Scaladoc with warnings that some operations require POSIX filesystem.
• better-files uses implicits everywhere to pass around the preference on whether the symbolic links should be followed etc, but seems to be planned to remove all implicits in 4.0.0. sbt IO also removes the implicits by creating two datatypes RichFile and LinkOptionPath.
• My implementation is in an universal trait, partly because sbt.io.RichFile is a value class. This means File to NIO Path is happening on all operations. To cache Path like better-files's File, use LinkOptionPath.
• Fixes the name isOtherReadable to isOthersReadable, following the NIO flag name.
• Adds test for underlying filesystem such as IO.isPosix and IO.hasAclFileAttributeView.
• In addition to IO.chmod(..), IO.chown(..) adds English name IO.setPermissions(..), IO.setOwner(..) following the sbt IO convention.

caveat

These will become new methods added to our API, so if a plugin starts using them it will bump up the minimum required sbt version to whichever that shipped this change. Thus, we should ship in a feature release 1.1.

[typesafe-tools]

The validator has checked the following projects against Scala 2.12,
tested using dbuild, projects built on top of each other.

Project	Reference	Commit
sbt	1.x	sbt/sbt@34945af
zinc	1.x	sbt/zinc@ef3a2c4
io	pull/76/head	71bd6ca
librarymanagement	1.x	sbt/librarymanagement@0419371
util	1.x	sbt/util@cba6f83
website	1.x

❌ The result is: FAILED
(restart)

[muuki88]

Nice 😎