Add addHosts/delHosts methods

[kirill-k-roxot]

Hello!

Let me thank you in public for such a simple yet great tool.

I updated the code, the changes are following:

• added addHosts and delHosts method, allowing to specify just the record to add, not the full list, as setHosts demands
• added internal _elements_names_fix method to allow use both Name / HostName and Type / RecordType filed name pairs
• updated tests accordingly
• updated README.md with basic usage examples of new methods

The reason files looks ~95% rewritten are pep8/markdown warnings:

• replaced tabs with 4x white-spaces
• replaced def x(a = 1) with def x(a=1)
• replaced { a: 5 } with {a: 5}

In fact, only 2 stated methods were added.

Feel free to review the code and comment if you want me to rollback some changes I made.

[kirill-k-roxot]

I also added CLI tool to simplify records management.

Let me know if you'd like to merge it in.

[kirill-k-roxot]

Added both new methods and CLI tool.

Thanks!