Hardcopy of pybind11 instead of using git submodules (#552)

* removed pybind as submodule
* added hardcopy of pybind11 2.10.0
* rename pybind11 folder to avoid conflicts when changing branch

Co-authored-by: Dhanya Thattil <dhanya.thattil@psi.ch>

libs/pybind/docs/installing.rst

@@ -0,0 +1,105 @@
+.. _installing:
+
+Installing the library
+######################
+
+There are several ways to get the pybind11 source, which lives at
+`pybind/pybind11 on GitHub <https://github.com/pybind/pybind11>`_. The pybind11
+developers recommend one of the first three ways listed here, submodule, PyPI,
+or conda-forge, for obtaining pybind11.
+
+.. _include_as_a_submodule:
+
+Include as a submodule
+======================
+
+When you are working on a project in Git, you can use the pybind11 repository
+as a submodule. From your git repository, use:
+
+.. code-block:: bash
+
+    git submodule add -b stable ../../pybind/pybind11 extern/pybind11
+    git submodule update --init
+
+This assumes you are placing your dependencies in ``extern/``, and that you are
+using GitHub; if you are not using GitHub, use the full https or ssh URL
+instead of the relative URL ``../../pybind/pybind11`` above. Some other servers
+also require the ``.git`` extension (GitHub does not).
+
+From here, you can now include ``extern/pybind11/include``, or you can use
+the various integration tools (see :ref:`compiling`) pybind11 provides directly
+from the local folder.
+
+Include with PyPI
+=================
+
+You can download the sources and CMake files as a Python package from PyPI
+using Pip. Just use:
+
+.. code-block:: bash
+
+    pip install pybind11
+
+This will provide pybind11 in a standard Python package format. If you want
+pybind11 available directly in your environment root, you can use:
+
+.. code-block:: bash
+
+    pip install "pybind11[global]"
+
+This is not recommended if you are installing with your system Python, as it
+will add files to ``/usr/local/include/pybind11`` and
+``/usr/local/share/cmake/pybind11``, so unless that is what you want, it is
+recommended only for use in virtual environments or your ``pyproject.toml``
+file (see :ref:`compiling`).
+
+Include with conda-forge
+========================
+
+You can use pybind11 with conda packaging via `conda-forge
+<https://github.com/conda-forge/pybind11-feedstock>`_:
+
+.. code-block:: bash
+
+    conda install -c conda-forge pybind11
+
+
+Include with vcpkg
+==================
+You can download and install pybind11 using the Microsoft `vcpkg
+<https://github.com/Microsoft/vcpkg/>`_ dependency manager:
+
+.. code-block:: bash
+
+    git clone https://github.com/Microsoft/vcpkg.git
+    cd vcpkg
+    ./bootstrap-vcpkg.sh
+    ./vcpkg integrate install
+    vcpkg install pybind11
+
+The pybind11 port in vcpkg is kept up to date by Microsoft team members and
+community contributors. If the version is out of date, please `create an issue
+or pull request <https://github.com/Microsoft/vcpkg/>`_ on the vcpkg
+repository.
+
+Global install with brew
+========================
+
+The brew package manager (Homebrew on macOS, or Linuxbrew on Linux) has a
+`pybind11 package
+<https://github.com/Homebrew/homebrew-core/blob/master/Formula/pybind11.rb>`_.
+To install:
+
+.. code-block:: bash
+
+    brew install pybind11
+
+.. We should list Conan, and possibly a few other C++ package managers (hunter,
+.. perhaps). Conan has a very clean CMake integration that would be good to show.
+
+Other options
+=============
+
+Other locations you can find pybind11 are `listed here
+<https://repology.org/project/python:pybind11/versions>`_; these are maintained
+by various packagers and the community.