fix submodule url

format: clang-format-12

update deprecations for C++14

interpreter: fix deprecation for python 3.9

ref. https://docs.python.org/3/c-api/init.html#c.PyEval_InitThreads:

> Changed in version 3.7: This function is now called by Py_Initialize(),
> so you don’t have to call it yourself anymore.

> Changed in version 3.9: The function now does nothing.

> Deprecated since version 3.9, will be removed in version 3.11.

Add fwd.hh header file.

Otherwise we can't include its fwd.hh

add missing include for Boost 1.76

[CMake] set INSTALL_RPATH for python on linux

To avoid the need to set `LD_LIBRARY_PATH` when the
`CMAKE_INSTALL_PREFIX` is not a standard one.

[Python] remove references to matlab, fix #73

[CI] drop travis, fix #65

Fix build on 16.04

On 16.04, fix:
…/dynamic-graph-python-4.0.0/src/dynamic_graph/dynamic-graph-py.cc: In function 'void exposeCommand()':
…/dynamic-graph-python-4.0.0/src/dynamic_graph/dynamic-graph-py.cc:191:24: error: 'raw_function' is not a member of 'bp'
.def("__call__", bp::raw_function(dg::python::entity::executeCmd, 1), "execute the command")
^

On 16.04, fix:
…/dynamic-graph-python-4.0.0/include/dynamic-graph/python/module.hh:47:26: error: 'exposeEntity' function uses 'auto' type specifier without trailing return type
inline auto exposeEntity() {
^