Add examples for printers

[S3v3ru5]

Added examples for each of the available printers (examples/printers). 4 files are added for each printer:

• .py: PyTeal implementation of the example contract.
• .teal: Compiled Teal code.
• .dot: Generated dot file by the printer.
• .png: Png of the dot file.

Examples are created for all the available printers:

• CFG
• Subroutine CFG
• Call graph
• Human Summary
• Transaction context

Some of these printers are not merged into dev. .dot and .png files might need to be regenerated for those printers.

NOTE: Examples in Printer Documentation use files from this branch. Do not delete this branch before updating the URLs in wiki

[S3v3ru5]

Merged into branch dev-sub-cfg PR #149