nemesit

Results 4 issues of nemesit

Would fix #1018

bug
rails-7-0

## Issue change_column_default and similar methods not working as intended ## Expected behavior according to the documentation [change_column_default](https://apidock.com/rails/ActiveRecord/ConnectionAdapters/SchemaStatements/change_column_default)(:users, :email, nil) `change_column_default("SomeTable", "SomeColumn", nil)` should drop the default constraint on SomeColumn....

The separators look quite jaggy on hi-dpi displays

It would be nice to have some basic syntax highlighting for markdown/multimarkdown in nvALT as it becomes difficult to read longer notes with a few links, heading, italics etc