Add library documentation

_book/06-installing-or-building-from-sources/05-library

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+---
+title: "Using as a library"
+---
+
+Verovio can be built and use as C++ or C library.
+
+### Building libverovio.so on Linux or libverovio.dylib on macOS
+
+```sh
+cd tools
+cmake -DBUILD_AS_LIBRARY=ON .
+make
+```
+
+Running `sudo make install` will copy the library and the headers in `/usr/local/lib` and `/usr/local/include/verovio` respectively.
+
+### Building verovio.dll on Windows using Microsoft Visual Studio Build Tools 2022
+
+In addition to Microsoft Visual Studio Build Tools 2022, also [Make](https://gnuwin32.sourceforge.net/packages/make.htm) is used.
+
+Open `x64 Native Tools Command Prompt for VS 2022` and enter:
+
+```
+cd cmake
+cmake -G "Unix Makefiles" -DBUILD_AS_LIBRARY=ON -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=TRUE .
+make
+```
+
+### Examples
+
+#### C++ interface
+
+The following code is a minimal example using the C++ Toolkit class:
+
+```cpp
+#include <iostream>
+using namespace std;
+
+// Include header for the vrv::Toolkit classl
+#include "toolkit.h"
+
+int main()
+{
+    vrv::Toolkit tk(false);
+    // Print the version
+    cout << tk.GetVersion() << endl;
+
+    return 0;
+}
+```
+
+The example can be built with:
+
+```sh
+g++ main.cpp -o main --std=c++17 -lverovio -I/usr/local/include/verovio
+```
+
+Running `./main` should display the Verovio version.
+
+### C function interface
+
+To use Verovio with any language that supports a plain C function interface you will first need to build Verovio as a library.
+The compiled library (`libverovio.so`/`verovio.dll`) will contain callable C symbols. These wrapper symbols are defined in `./tools/c_wrapper.h`
+
+## Complete example in C
+
+To run the `main.c` example you can use gcc to compile the example and link to the pre-built library.
+
+```sh
+gcc main.c -o main -L../../tools -lverovio
+```
+
+Run (without changing your default LD LIBRARY PATH):
+
+```sh
+LD_LIBRARY_PATH=../../tools ./main
+```