Add 'lint' command to validate messages

[rcmachado]

Add a lint command that could educate about best practices regarding changelog messages. One easy win would be checking for Add ..., Fix ..., Remove ... kind of messages in their respective sections.

Some examples:

• Add some interesting feature messages under Added section became Some interesting feature (since Added section already denotes it was added)
• Fixed issue that prevents something message under Fixed section became Issue that prevents something

Other issues it could check:

• Missing links for versions