Fix the index corruption (#81)

Add is_*type* functions

• Fixed Node.Clone() to update the correct parents for children

Fix the sum and avg functions for the only numeric value.

Fix the issue #67

Fixed error handling for cmd/ajson

• Add functions last, first, parent, root, and key
• Add multiline support for CLI

Fixes: #61

Add new functions:

b64decode    Base64 Decoding                string
b64encode    Base64 Encoding                string 
b64encoden   Base64 Encoding (no padding)   string

Fixed operation parser.