Add module to control chunk size.

enstools/encoding/chunk_size.py

+# Using a module file to store the desired chunk size.
+chunk_size = "10MB"
+
+def change_chunk_size(new_chunk_size: str):
+    global chunk_size
+    chunk_size = new_chunk_size
+
+# This variable will be used in many places.
+# One can modify this variable directly assigning a new value
+# enstools.encoding.chunk_size.chunk_size = "1MB"
+# or using the function change_chunk_size("1MB")
+