Add the Changelog for 0.6.2

Changelog

+CHANGELOG
+
+1. Clients API relies on objpool instead of snf-common for connection pooling
+2. MS Windows compatiblity:
+    * adjust pithos interface
+    * adjust pithos client local fs handling
+    * progress bar configuration not to rely on unicode characters
+    * adjust hidden Clients API unittests
+3. Update documentation:
+    * rearange text for easier setup
+    * document undocumented methods in Clients API and cli auxiliary methods
+    * MS Windows setup guide
+4. Improve interface output:
+    * detailed description mechanism
+    * uniformity between shell and one-command
+    * various command-specific improvements
+    * new print_list, print_dict and print_item methods have:
+        - better indentation 
+        - enumeration flag
+        - redundancy of presented information flag
+    * mechanism for more descriptive syntax errors and arguments help
+5. Improve error handling:
+    * concrete mechanism for client error propagation
+    * catch some unhandled errors
+    * mechanism for detailed error descriptions
+    * context-specific errors
+    * showcase error handling in store_list
+6. CLI Code restructure:
+    * Introduce ArgumentParseManager class to manage argument parsing
+    * Introduce a seperate one_command package for handling one_command
+    * clean-up main CLI code (move interface-specific methods to their pckgs)
+7. New history capabilities:
+    * allow command ranges
+    * allow backward counting
+    * in-shell sequensial script-like execution of previous commands
+8. Minor new features:
+    * store_publish returns publication url
+    * store_list can list with prefixes instead of full path
+    * hidden optional testing of quoted text and cli.utils.print_* methods
+    * shell prompt easy to modify
+9. Bugfixes:
+    * Shell does not repeat previous command in case of error
+    * handle ValueErrors and KeyErrors
+    * config set values are effective immidiately
+    * unwanted argument inheritance in shell, removed