enh: linear and efficient neighbour finder

src/sisl/CMakeLists.txt

@@ -11,3 +11,4 @@ endforeach()
 # Add other sub-directories
 add_subdirectory("io")
 add_subdirectory("physics")
+add_subdirectory("geom")

src/sisl/geom/CMakeLists.txt

@@ -0,0 +1 @@
+add_subdirectory("neighs")

src/sisl/geom/__init__.py

@@ -51,3 +51,4 @@
 from .nanotube import *
 from .special import *
 from .surfaces import *
+from .neighs import *

src/sisl/geom/neighs/CMakeLists.txt

@@ -0,0 +1,19 @@
+# In this directory we have a set of libraries
+# We will need to link to the Numpy includes
+set_property(DIRECTORY
+  APPEND
+  PROPERTY INCLUDE_DIRECTORIES
+  ${CMAKE_CURRENT_SOURCE_DIR}/..
+  )
+
+foreach(source 
+    cneighs
+    )
+  add_cython_library(
+    SOURCE ${source}.pyx
+    LIBRARY ${source}
+    OUTPUT ${source}_C
+    )
+  install(TARGETS ${source} LIBRARY
+    DESTINATION ${SKBUILD_PROJECT_NAME}/geom/neighs)
+endforeach()

src/sisl/geom/neighs/__init__.py

@@ -0,0 +1 @@
+from .neighfinder import NeighFinder