Implement cmake file for installation and external use

[sbaldu]

Add a CMake file that allows to import the library in two ways:

• install using cmake -B build && sudo cmake --install build
• clone inside of the project directory or add as git submodule
  In the two cases the CMake file looks like:

# option 1
find_package(xtd REQUIRED)
#option 2
add_subdirectory(xtd)

add_executable(main.out main.cpp)
target_link_libraries(main.out xtd)

Also fix some typos in sin.h

[fwyzard]

I am very much not a fan of CMake.

Will get back to this PR once I've digested it better :-)