Add support for MarkDown headings formatted as "COMMAND(1) ..."

[thaJeztah]

relates to spf13/cobra#1049 and docker/docker-ce-packaging#502

[thaJeztah]

ping @cpuguy83 @tianon PTAL

[thaJeztah]

hm, actually, more may be needed for cobra, as I think it's using % COMMAND(1) (so not a heading)

[thaJeztah]

So, after digging why it didn't work with the % xxx pandoc headers, this seemed to be the problem; the tests were running without the blackfriday.Titleblock extension enabled, so blackfriday was not converting them to H1 blocks.

[thaJeztah]

@cpuguy83 @tianon this should be ready to go now. I noticed that v1 would convert this input;

% DOCKER(1) Docker User Manuals
% Docker Community
% JUNE 2014

To:

.TH "DOCKER" "1" " Docker User Manuals" "Docker Community" "JUNE 2014"
.nh
.ad l

And v2 (with this change applied) converts it to:

.nh
.TH DOCKER 1 Docker User Manuals
Docker Community
JUNE 2014

As a result, the words were split, and didn't show up correctly when viewing the man page;

With V1:

man ./v1.1

DOCKER(1)                                                                              JUNE 2014                                                                              DOCKER(1)

Docker Community                                                                   Docker User Manuals                                                                        DOCKER(1)

With V2:

man ./v2.1

DOCKER(1)                                                                               Manuals                                                                               DOCKER(1)

Docker Community JUNE 2014

User                                                                                     Docker                                                                               DOCKER(1)

I pushed another commit to remove newlines, and to quote each line. It's a bit ugly, so better suggestions welcome

[cpuguy83]

Is this still needed?

[cpuguy83]

@thaJeztah ?

[thaJeztah]

I guess with the fix in Cobra, it's no longer needed; let me close this one (I'll keep the branch for now, in case we find we still need it)