Imported libSDF into VOID tree

external/libsdf/libSDF/dictionary

@@ -0,0 +1,54 @@
+This is a dictionary of "known" names in nbody files.
+It will be extended as the need arises.
+
+The first few come from the headers:
+
+float npart
+float iter
+float time
+float ke
+float pe
+float masstot
+float l_ang
+float Gnewt
+float epsilon
+float zinitial
+float omega
+float hubble
+float box_size
+float znow
+float initial_rsize
+float initial_rmin_x
+float initial_rmin_y
+float initial_rmin_z
+float veltime
+float sizeof_ext
+float alpha
+float beta
+float curvature
+float lambda
+float cosm_integral
+float radius
+int int_npart
+int int_sizeof_ext
+char tree_header_text[384];
+
+The following arrays are of length (int)nbody.  Unfortunately,
+in order to maintain historical compatibilty, the length of the
+array is stored as a binary float in the files, so consider using
+nbio_rd_double(..., "nbody") to figure out how long these vectors are.
+
+float x[], y[], z[]
+float vx[], vy[], vz[]
+float mass[]
+
+From the msw .ap files, we also have
+float acc[]
+float phi[]
+
+Presumably, we should also reserve:
+float ax[], ay[], az[]
+
+The char id[][4] is specified by tree and tree_ap files.
+
+There will undoubtedly be others.