Enable c++11 compilation and use a few of the features.
Fix .cbp syntax.
Convert options table to an unordered map.
Fixes to make compilation work with c++11. (#7626)
ssize_t was more trouble than it was worth.
Include iterator to make VC happy.
Apply namespacing correctly for pow to handle more pedantic compilers, and shuffle around types used to take advantage of new type promotion rules.
Fix compile errors under mingw-w64.

To be included in PR #7626.
Apply the main CXXFLAGS to `make json-check`.

In particular, do apply --std=c++11 to chkjson, but including the rest
of the flags shouldn't hurt.
Merge remote-tracking branch 'dda/pr/7626' into dda-master

* dda/pr/7626:
  Apply the main CXXFLAGS to `make json-check`.
  Fix compile errors under mingw-w64.
  Apply namespacing correctly for pow to handle more pedantic compilers, and shuffle around types used to take advantage of new type promotion rules.
  Include iterator to make VC happy.
  ssize_t was more trouble than it was worth.
  Fixes to make compilation work with c++11. (#7626)
  Convert options table to an unordered map.
  Fix .cbp syntax.
  Enable c++11 compilation and use a few of the features.

Conflicts:
	src/item.cpp