Adding deprecation decorators from astropy

[bsipocz]

As we discussed in #1430, these decorators from astropy are very handy to deprecate keywords and methods. Handling the case of removing kwarg was added in version 2.0.12 and 3.1.2, so we need to keep these around in astroquery until the minimum required version covers these.

@keflavich - what do you think, should these live in an extern directory or directly in utils? These are around for astroquery internal usage only, so we may not even need the changelog entry.

[codecov]

Codecov Report

Merging #1435 into master will decrease coverage by 0.37%.
The diff coverage is 12.08%.

@@            Coverage Diff             @@
##           master    #1435      +/-   ##
==========================================
- Coverage   64.92%   64.54%   -0.38%     
==========================================
  Files         165      166       +1     
  Lines       12820    12911      +91     
==========================================
+ Hits         8323     8334      +11     
- Misses       4497     4577      +80

Impacted Files	Coverage Δ
astroquery/utils/decorators.py	12.08% <12.08%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d6584e8...9f2dc5b. Read the comment docs.

[keflavich]

It's fine as you've done it.