add bulk operations: create, update, delete; and find_or_create + count methods for single records

[Yevhenii-Kushvid]

In recent project I faced the issue of performance, and found in AriTable api bulk operation: here is my proposal implementation of them for airrecord gem.

• Table#bulk_create
• Table#bulk_update
• Table#bulk_delete

and additional helper for record finding

• Table#find_or_create
• Table#count

link to API documentation