Added HeadingInfo.Default and CopyrightInfo.Default.

HeadingInfo.Default exposes the default heading generated by
HelpText.AutoBuild.
Sensible defaults have also been added, removing the need to explicitly
add assembly attributes (though they still take precedence).

CopyrightInfo.Default exposes the default info generated by
HelpText.AutoBuild.
Similar to HeadingInfo.Default.

Also fixes bug #22.
Merge with master.
Merge with upstream/master.
Removed properties added by mistake during merge.
Merge pull request #25 from mizipzor/helptext

Added HeadingInfo.Default and CopyrightInfo.Default.