feat: new library Flow Chart Symbols

[excalibot]

Common symbols used in flow chart, including: Start / End, Process, Decision, Document, Multiple Document, Manaual Input, Predefined Process, Input / Output, And, Or, Database, Preparation / Initialization, Delay, Connector, Off-page Connector

Submitted by @finfin

Items: Off-page Connector, Connector, Delay, Preparation / Initialization, Database, Or, And, Input / Output, Predefined Process, Manaual Input, Multiple Document, Document, Decision, Process, Start / End

Installation link