Add deprecation message to polynomial pointer, order constructor

[mborland]

Now that we require C++14 this is an easy fix @NAThompson.
Closes #156

[NAThompson]

@mborland : Any reason this didn't get merged?

[mborland]

@mborland : Any reason this didn't get merged?

Some of the old compilers don't support deprecated messages on classes if I remember correctly.

[NAThompson]

@mborland : Have we dropped support for the old compilers yet?

[mborland]

@mborland : Have we dropped support for the old compilers yet?

I think so. I'll have to rebase this onto develop to confirm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.41%. Comparing base (3c1c431) to head (74e3386).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #974   +/-   ##
========================================
  Coverage    95.40%   95.41%           
========================================
  Files          831      831           
  Lines        69540    69550   +10     
========================================
+ Hits         66346    66360   +14     
+ Misses        3194     3190    -4     

Files with missing lines	Coverage Δ
include/boost/math/tools/polynomial.hpp	99.27% <ø> (ø)

... and 3 files with indirect coverage changes

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