Julia: rename mx.clip to clamp for NDArray

[iblislin]

• in order to match Base interface

• depwarn for mx.clip included

Checklist

• Changes are complete
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

[eric-haibin-lin]

Hi, what is the motivation for renaming the API?

[iblislin]

There is a API named clamp, which functionality is same as mx.clip, in Julia's stdlib.

e.g.

julia> A = [1,2,3,4,5]
5-element Array{Int64,1}:
 1
 2
 3
 4
 5

julia> clamp.(A, 3, 4)
5-element Array{Int64,1}:
 3
 3
 3
 4
 4

So I renamed and make it overload the clamp function for type NDArray.

[vandanavk]

@mxnet-label-bot add [pr-awaiting-review]

[larroy]

Why not leave both?

[iblislin]

I'm ok if making aliasing is an acceptable option.

[larroy]

LGTM, this is a matter of taste, so up to @iblis17

[wkcn]

This PR has been merged.
Thanks for your contribution!