Merge remote-tracking branch 'upstream/master'

Conflicts:
	local-io/local-io.asciidoc
Update 'read keystroke' recipe in local-io.

Responded to Ryan's and Colin's comments.  Note that this version has a footnote which, when HTML output is produced, renders at the end of the entire HTML document (i.e. the end of the book), but which should render properly at page bottom in PDF output (which I haven't gotten working yet in my asciidoc installation).
Clarify what the standard deviation is.

Also include a link to the Wikipedia site for Standard deviation.
Fix grammatical error.
Merge pull request #52 from hyPiRion/standard-deviation

Clarify what the standard deviation is. Ref #14 and #2.
Merge #53
First version of Get files from a directory
First version of delete file
First version of copy file
First version of file properties
Update CONTRIBUTING.md to specify canonical location of recipe files
Merge pull request #61 from jcromartie/instructions

Update CONTRIBUTING.md to specify canonical location of recipe files
Adds recipe for reading/writing clojure data structures on disk
Adds read/write clojure data to Local IO chapter file
Adds note pointing to read-write-files
Revises local-io/read-write-files recipe to be more explanatory
Updated with feedback
Update CONTRIBUTING.md to specify canonical location of recipe files
Adds license assignment for jcromartie
Merge pull request #65 from jcromartie/attribution

Adding my attribution