add four Rcpp::Shield<>() to make rchk even happier

[eddelbuettel]

No description provided.

[codecov-io]

Codecov Report

Merging #79 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #79   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           5      5           
  Lines         222    225    +3     
=====================================
+ Hits          222    225    +3

Impacted Files	Coverage Δ
src/anytime.cpp	100% <100%> (ø)	⬆️

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