try to remove invalidations

[jverzani]

Another attempt to close issue #403

• removed spurious module name from abstract type with PnPolynomial constructor
• relaxed signature of any to avoid base method which defined method for ismissing.

fingers crossed

[codecov]

Codecov Report

Merging #421 (016b873) into master (d0cd9d3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #421   +/-   ##
=======================================
  Coverage   83.70%   83.70%           
=======================================
  Files          23       23           
  Lines        2798     2798           
=======================================
  Hits         2342     2342           
  Misses        456      456           

Impacted Files	Coverage Δ
src/polynomials/pi_n_polynomial.jl	77.77% <ø> (ø)
src/common.jl	89.63% <100.00%> (ø)

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