Improved exception infrastructure

[coatless]

This is PR 2 of 3.

Contained within this PR is the necessary upgrade to the exception infrastructure to proceed with improving internal exception messages.

The third PR aims to provide the improved internal exception messages based on the proposal table in #184.

(The first PR was the upstream refresh of the tinyformat library.)

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Changes:

• Added local mod in tinyformat to enable variadic templates if C++11 is detected.
• Created a C++11 exception message version using variadic templates for Rcpp::stop, Rcpp::warning, and RCPP_ADVANCED_EXCEPTION_CLASS
• Added C++98 exception message version using generated macro arguments.
• Extracted generated Rcpp::stop and Rcpp::warning functions from exception.h and moved them into C++98 exception header
• Modified RCPP_EXCEPTION_CLASS macro to have a default ctor that returns a default constructed string to allow for promotion without breaking present use.
• Promoted no_such_slot and not_a_closure to use RCPP_EXCEPTION_CLASS from RCPP_SIMPLE_EXCEPTION_CLASS.
• Promoted index_out_of_bounds and not_compatible to use RCPP_ADVANCED_EXCEPTION_CLASS.
• Flagged no_such_field and reference_creation_class for potential removal.

[codecov-io]

Codecov Report

Merging #676 into master will decrease coverage by 0.02%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #676      +/-   ##
==========================================
- Coverage   92.91%   92.88%   -0.03%     
==========================================
  Files          65       65              
  Lines        3302     3303       +1     
==========================================
  Hits         3068     3068              
- Misses        234      235       +1

Impacted Files	Coverage Δ
inst/include/Rcpp/exceptions.h	50% <50%> (-50%)	⬇️

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[eddelbuettel]

Looks good to me at first glance.

Reverse depend check running too.

[eddelbuettel]

It seems to make some noise in other project though ... when -pedantic -Wextra is used. Falling back to -Wno-unused quiets it down a little.

[coatless]

Modifications to the C++98 macro to remove ; were done in:

e08d088 and 138454e