Convert non-breaking space to ~

LaTeX chokes on \nolinebreak{} if there is no line to end. ~ adds a 'normal' space, makes no trouble with empty lines, and generally fits the concept of a non-breaking space.
Updated benchmark script to output relative times in respect to kramdown
Added link to list of libraries on wiki
Merge branch 'master' of https://github.com/hperl/kramdown
Added Utils.snake_case for making a snake_case version of a CamelCased one
Try requiring a parser/converter library based on the specified input/output name

Fixes GH issue #51
Updated codeblock regexp to avoid long regexp running times, fixes GH#45

This also affects footnotes since they use the regexp from the
codeblocks.
Updated release notes, version and homepage