Install pywrapper.h alongside symengine/lib/symengine.pxd

This is a better option than PYTHON_INSTALL_HEADER_PATH which
doesn't work everywhere and recent cython supports this change

Author: isuruf

symengine/lib/CMakeLists.txt

@@ -35,3 +35,8 @@ install(FILES __init__.py
     symengine_wrapper.pxd
     DESTINATION ${PY_PATH}
     )
+
+install(FILES
+    pywrapper.h
+    DESTINATION ${PYTHON_INSTALL_PATH}/symengine/lib
+    )

symengine/lib/symengine/pywrapper.h renamed to symengine/lib/pywrapper.h

@@ -294,7 +294,7 @@ cdef extern from "<symengine/number.h>" namespace "SymEngine":
     cdef cppclass NumberWrapper(Basic):
         pass
 
-cdef extern from "<symengine/pywrapper.h>" namespace "SymEngine":
+cdef extern from "pywrapper.h" namespace "SymEngine":
     cdef cppclass PyNumber(NumberWrapper):
         PyObject* get_py_object()
     cdef cppclass PyModule:
@@ -304,7 +304,7 @@ cdef extern from "<symengine/pywrapper.h>" namespace "SymEngine":
     cdef cppclass PyFunction:
         PyObject* get_py_object()
 
-cdef extern from "<symengine/pywrapper.h>" namespace "SymEngine":
+cdef extern from "pywrapper.h" namespace "SymEngine":
     cdef cppclass PySymbol(Symbol):
         PySymbol(string name, PyObject* pyobj)
         PyObject* get_py_object()