add: support wstring constructor.

fix: return nullptr.

update README.md

support _ini[section][key]=value;

mod: to keep simple,let 'modify' as 'set'

Update main.cpp

Update main.cpp

Solve the read-only issue of the configuration file.

Simplified example/main.cpp and Added New Features,see README.md

add start history

Disable std::wstring by default, as not all C++11 compilers support <codecvt>.

support value with space and tab

format inicpp.hpp

Update README.md

Update README.md