Add ignore_mailto_links config option

[gpanders]

This is useful when converting HTML emails to text. Generally,
there's no reason to preserve these links when sending email.

[coveralls]

Coverage increased (+0.01%) to 97.075% when pulling 936e8eb on gpanders:ignore-mailto-links into e3ea63c on Alir3z4:master.

[coveralls]

Coverage increased (+0.01%) to 96.824% when pulling 28945e6 on gpanders:ignore-mailto-links into 4592133 on Alir3z4:master.

[Alir3z4]

I checked by sending plain/text email and opened the same email in Gmail and Thunderbird and also Windows Mail. Even though the email was plain text, they would make it clickable by doing mailto:xxx

Considering the above, would there be still a reason to remove them before sending?

[gpanders]

Considering the above, would there be still a reason to remove them before sending?

I use html2text in my mail client to convert HTML emails into plain text so that I can then respond to them in plain text. There is no reason to linkify email addresses in a plain text email. Consider:

Please email me at [greg@example.com](mailto:greg@example.com).

So the ability to strip these out is useful for those of us who send and receive emails in plain text.

[Alir3z4]

Yeah, makes sense.
Let me fix the conflict and get it merged.