Add prime-number spirals post with YAML matter.

_posts/2014-10-01-prime-number-spirals.md
	-Add the file for the prime-number spirals post.
	-Add YAML matter.
Add prime-number thumbnail; downsize power-set img.

img/thumbnails/power_set.png
	-Decrease to 100x100 pixels in size, my blog's new thumbnail
	standard.

img/thumbnails/prime_number_spiral.png
	-Add a thumbnail for the prime-number spirals post.
Write up Ulam/Sacks spiral, and math background.

_posts/2014-10-01-prime-number-spirals.md
	-Illustrate the history behind the Ulam and Sacks spirals.
	-Explain prime-generating polynomials, and how they tie into
	prime-number spirals.
Write up algorithms for rendering both spirals.

_posts/2014-10-01-prime-number-spirals.md
	-Write up the canvas setup necessary to render the spirals.
	-Describe the Ulam/Sacks algorithms, and provide code for each.
Make final textual edits/quality approval.

_posts/2014-10-01-prime-number-spirals.md
	-Make some stylistic textual edits/check hyperlinks/etc.
	-Add an additional footnote about Ulam.
Add prime-spirals code and download link.

_posts/2014-10-01-prime-number-spirals.md,
downloads/prime_number_spirals.zip
	-Add zipped code for the
	`_posts/2014-10-01-prime-number-spirals.md` post.
	-Add a download/Github link to it.
Add prime-number spiral post images.

img/prime_number_spirals/
(big_sacks_spiral, big_ulam_spiral, small_ulam_spiral).png
	-Add images linked to by the prime-number spirals post.
Isolate smooth-scroll inclusion to _include.

(_includes/smooth_scroll, _layouts/post).html
	-Create an includable snippet to link in and configure the
	smooth-scroll library, as it will be used on pages besides
	posts.
Add smooth-scroll to post footnotes/blog tags page.

_plugins/external_plugins/(tag-cloud, tocGenerator).rb
	-Add smooth-scroll to blog footnotes and elements on the tags
	page.
One-liner: modify a tag in prime-spirals post.

_posts/2014-10-01-prime-number-spirals.md
	-Use plural "prime numbers" instead of the singular.
Merge branch 'post/prime_number_spirals'

_posts/2014-10-01-prime-number-spirals.md
	-Write a post about the history of prime-number spirals, some of
	the math behind them, and algorithms to render the Ulam and
	Sacks spirals.