Add cmake install support

[schultetwin1]

This change adds an install step to the CMake build system. This will allow other users of CMake to easily integrate ELFIO with their projects without any extra work. This is also the first step to be able to distribute ELFIO via vcpkg.

The benefit of this is, after building using CMake and then running make install with ELFIO users of CMake can then use the following CMake to easily pull in ELFIO.

find_package(elfio REQUIRED)

add_executable(my_example_exe ....)
target_link_libraries(my_example_exe PRIVATE elfio::elfio)

List of changes

• Remove the setting of CMAKE_CXX_STANDARD to 17. elfio headers do not require C++17.
• Add options to enable building of examples and tests (off by default).
• Parse out elfio version from elfio_version.hpp
• Create a elfio target, which properly sets up header include paths for the examples and tests
• Install the elfio target to be used by external consumers of elfio
• Enable tests to run under ctest (so you can run make and then make test)

[schultetwin1]

@serge1 if you aren't interested in this change feel free to close it. My main goal is to be able to include ELFIO as a package in vcpkg to make it easier for downstream consumers to use ELFIO.

[serge1]

Thank you for your submission! I will look at it soon

[serge1]

Hi Matt, I definetly accept your changes - they are very beneficial for the library. Thank you!

When using GNU make generator, do you know what should be configured to have 'make check' working together (or instead of) 'make test'?

[schultetwin1]

Hi Matt, I definetly accept your changes - they are very beneficial for the library. Thank you!

When using GNU make generator, do you know what should be configured to have 'make check' working together (or instead of) 'make test'?

I do! I just created #51 to do that