Processpiper

* Fixed [17](https://github.com/csgoh/processpiper/issues/17) : Connections appear to be going at the wrong direction.
* Used `rich` package to improve debug message readability.

- Revamped elements placement logic. The code is much easier to maintain and the display layout is more compact.
- Added collision detection logic. The connect lines would now avoid overlapping with element shape. It is not perfect, but hopefully it is a step in the right direction.
- Enhanced English like `PiperFlow` syntax. You can now specify `width` in the syntax.
- Cleaned up code further.

* Removed the dependency of Arial font on Linux system. i.e. The following commands to install MSCoreFonts is no longer required.
* sudo apt install ttf-mscorefonts-installer
* sudo fc-cache -f
* Added Message, Signal, Conditional and Link event types
* Added Event gateway type
* Code clean up

- Added '' comment line to text2diagram method
- Calling render() method without providing output file name will not result in random png file generated

- Added validation and exception messages when pool, lane, element or connection are not added to the diagram.
- text2diagram.render() now return generated code and the diagram in PIL.Image format
- Accommodate for extra tabs, spaces and newline characters when generating diagram using plain text method.

Able to add connection label when rendering diagram with text2diagram library. Eg: login-"credentials"->display_dashboard