Resolve issue #526

[jasjuang]

With this addition of cmake export, users can now use find_package(tinyxml2) in config mode, meaning no more Findtinyxml2.cmake is needed!!

To demonstrate the convenience of this feature, first clone, build, and install tinyxml2

git clone https://github.com/jasjuang/tinyxml2
cd tinyxml2
mkdir build
cd build
cmake ..
sudo make install

Now go to your own repo and then create a CMakeLists of your own that looks something like

cmake_minimum_required(VERSION 3.5)
project(tinyxml2Example)

set(PROJECT_SRCS
${PROJECT_SOURCE_DIR}/tinyxml2Example.cpp
)

find_package( tinyxml2 REQUIRED )

add_executable(${PROJECT_NAME} ${PROJECT_SRCS})

target_link_libraries(${PROJECT_NAME} tinyxml2)

That will just work! A step by step to reproduce this will be something like

mkdir mytestrepo
cd mytesttrepo
touch CMakeLists.txt 
# use your favorite text editor to copy paste the above in
touch tinyxml2Example.cpp
# use your favorite text editor to add in some tinyxml2 code
mkdir build
cd build
cmake ..
make

[comargo]

As I understand, the Export installation path should be LIBDIR/cmake/PROJECT_NAME

[jasjuang]

@comargo which I did in line 166~171. This line just export the targets locally and not installing yet

[comargo]

Ah! Sorry... I missed the name of variable...

[jasjuang]

@leethomason Could you merge this and make a release? This feature is necessary for integration to vcpkg. Thanks

[jasjuang]

@leethomason Could you make a release? I will submit a pull request to vcpkg once you make a release, thanks!

[leethomason]

There's another PR going in, and then I'll do a release.

[jasjuang]

@leethomason Thanks for the release. I submitted a PR to vcpkg and once it's merged Windows users will be able to build and install tinyxml2 by simply typing vcpkg install tinyxml2!