Add picture for Lincoln Mullen

Here is the text for the bio:

Lincoln is an assistant professor of history at George Mason University.
He maintains the gender package.
added help details to resources page, including SO link #32
draft post on Docker
fixed a few typos
add plug for analogsea
Added cropped png
Deleted jpg file
Added Lincoln to the community page. #93
Completes PR #93
Implements all the great edits suggested by @karthik & @sckott
p.s. @sckott good call on the open source -- yup, it's Apache 2.0, I added a link to the license on the github page for the source code
new version of Docker blogpost
update author metadata
fix metadata formatting (was probably reponsible for the rendering issues), also a few minor updates to text for slightly better flow
Added a few comments inline (feel free to use/discard).
another small fix. s/hadleyverse/Hadleyverse
add cross-link to Dirk's blog
Merge branch 'cboettig' of github.com:ropensci/roweb into cboettig
fixes additional little things marked by Karthik (Thanks!)
in the require call, nokogiri should be lowercase
fixed link