Merged big PR #17 (Contributed by @ray-g. Thank you!)
- Resolved issue-10, integrated with dot command
- Resolved issue-14, replace the illegal characters in the table name, which I have the same requirement
- Resolved issue-16, make the isolated node horizontal, which I also have the same requirement
- Added colors segment, which can act as a named color palette
- Added ? mark to the cardinality, showing the {0,1}, which exists in the BurntSushi ER format
- Cleaned some lint issues in go and markdown files.