Rename has-matching-part? "needs-matching-part?."

has-matching-part? suggests a left- that already has a right.
Rename matching-part make-matching-part.
Spelling error.
Add valid move to pegthing example.
beginning to make the switch
more progress on nav
previous and next
add breakpoint
beginning to make responsive
Merge pull request #48 from ssorc/master

Corrected typos and omissions in the 'Core Functions in Depth' chapter
responsiveness working
more layout tweaks
another layout tweak of page leader
updated nanoc process
toc
toc filter working, misc tweaks
more toc tweaks
more little tweaks
and more tweaks
Merge branch 'bredesign'