gnsync create/update files in "plain" or "markdown" format

[chamot1111]

Hi,

Some of my notes in Evernote are wrote in markdown format. When I used gnsync -t TWO_WAY, all the markdown is escaped. The format parameter has no impact on this.

This pull request take into account the format parameter. If format is plain, the result file is not transform using html2text.

As the default format is "plain", if the format was not force by the parameter in the command line, the program's behavior is change.

[weakish]

The format parameter has no impact on this.

--format is "in what format to save the note".
(--two-way is still undocumented.)

As the default format is "plain",
if the format was not force by the parameter in the command line,
he program's behavior is change.

This breaks backward compatibility.
What about add an additional option, e.g. --in-format?