Prepare for version 2.10.0 release

[smithsz]

2.10.0 (2018-09-19)

• [NEW] Add custom JSON encoder/decoder option to Document constructor.
• [NEW] Add new view parameters, stable and update, as keyword arguments to get_view_result.
• [NEW] Allow arbitrary query parameters to be passed to custom changes filters.
• [FIXED] Case where an exception was raised after successful retry when using doc.update_field.
• [FIXED] Removed unnecessary request when retrieving a Result collection that is less than the 'page_size' value

[ricellis]

Suggest correcting the markdown formatting on the page_size in the last [FIXED] entry.