Fix links to IPython config docs and try to clarify what needs to be done

I found this section confusing so I tried to improve it.  Not sure if it is correct for Windows though...
Fixed grammar and link to stable docs (instead of dev)
overwrite KernelManager.kernel_cmd if it has been changed (e.g. if the path to Julia changes), so that users no longer need to delete .ipython/profile_julia to reconfigure
libjulia-release -> libjulia.
Merge pull request #79 from nfoti/master

libjulia-release -> libjulia
Pkg2 -> Pkg
rm trailing whitespace from match (since on Windows there is a trailing \r)
Merge pull request #78 from GlenHertz/patch-1

Fix links to IPython config docs and try to clarify what needs to be don...
backwards compatibility for pending mimewritable API change
updated README
layout logics for julia mode
Merge pull request #89 from Carreau/ijm

layout logics for julia mode
overwrite config files if they have changed
tweaks to copy_config in build script
force re-highlighting of codecell after julia-mode loading
Merge pull request #95 from Carreau/re-hilight

force re-highlighting of codecell after julia-mode loading
added julia syntax highlighting. Implements #17
added support for symbols to julia notebook syntax highlighting
fixed misinterpretation of ' as string delimeter instead of transpose in notebook syntax highlighting
logging call removed from custom.js, mkpath factored out in build.jl