Fix amount of entries in the json object

After the initial j.push_back() calls there is another j.emplace_back() call that makes the size == 4 not 3.

Better diagnostics

 Conflicts:
	include/nlohmann/detail/input/parser.hpp
	single_include/nlohmann/json.hpp

Fix missing 1.78 in example in README.md

Co-authored-by: Alexander Karzhenkov <karzhenkov@mail.ru>

Add GDB pretty printer

readme: fix tilde character display