Before this patch, `basic_json` types with different template arguments
were treated as `CompatibleArrayType`. Which sometimes leads to recursive
calls and stack overflows.
This patch adds a constructor and a `get` overload to deal with
different `basic_json` types.
When building code relying on this library in Xcode, the build process throws an error (not a warning!) stating its inability to locate the presumed system includes. The `<>` angle brackets on `#include` indicate a system-level include, not a user-level include. By swapping to quotation marks for the `#include` we more accurately represent the content of the included files and Xcode builds without complaint!
Beside the fix discussed in #961, we also had to re-adjust a test case. It seems that it was failing before, and I "fixed" it to work with the broken implementation...
- updated documentation wrt. new repository layout
- temporarily switched off Homebrew --HEAD building (can only be switched on after release)
- set copyright date to 2018
* Rename 'develop' folder to 'include/nlohmann'
* Rename 'src' folder to 'single_include/nlohmann'
* Use <nlohmann/*> headers in sources and tests
* Change amalgamate config file
