Add more vertical spacing to KLib dumps

[fzhinkin]

Additional newlines should improve dump's readability and also improve diffs generated by the GH.

This change builds on #197, which groups declarations based on their kind.

Now, an extra newline will always be inserted before:

• // Targets: meta-header,
• a new class/interface/object/enum-class declaration
• in-between two declarations having different kinds (for example, between a group of vars and funs).

Closes #196