Support username password login.

See #21, release log:

• c5a0710 by @rultor: Merge remote-tracking branch '...
• 63ca8a8 by @Suseika: Fix todo indentation
• 51d0617 by @Suseika: Indent puzzle
• 055c335 by @Suseika: No line - no problem
• da9baac by @Suseika: Add the space PDD was complain...
• fbe49ef by @Suseika: Remove a line PDD was complain...
• ffeca7f by @Suseika: Remove extra try/catch block
• f91896e by @Suseika: Default visibility for Executi...
• e00c35b by @yegor256: gitattributes
• fd9c9ca by @yegor256: gitattributes
• 34f440f by @yegor256: #24 no-arg ctor for SSHD
• 4677461 by @Suseika: Fix todo
• a45753c by @Suseika: Fix todo indentation
• 9feda44 by @Suseika: Fix todo
• fe87052 by @Suseika: Add todo for extraction of Com...
• e4d4423 by @Suseika: Proper todo
• a28fd25 by @Suseika: Tests for Execution and SSHByP...
• 3fa89b1 by @Suseika: Make Execution an interface; a...
• 78958b3 by @Suseika: Annonate SSHByPassword with Lo...
• eb0ac2a by @Suseika: Merge short lines in Execution
• and 33 more...

Released by Rultor 1.56, see build log