Binned locus length vs % coverage QC plot

More clear than the non-binned version previously implemented.
chipenrich, broadenrich, and chipapprox are multicore

We implemented multicore versions of the chipenrich, broadenrich, and
chipapprox methods using the multicore R package. Note, Windows does
not support the multicore R package, so these methods will run as
single core for Windows users.

Bug fix: A ‘continuity gene’ was introduced for genesets if all genes
in the geneset had a peak to help the logistic regression converge. The
‘continuity gene’ mistakenly persisted for all genesets thereafter,
rather than only for the required geneset, slightly altering enrichment
p-values. This is no longer the case.
multicore and plotting changes

To avoid having to add multicore to the NAMESPACE, which is not
supported in Windows, the library is loaded within the functions which
use it.

plot_gene_versus_coverage() and ..plot_gene_versus_coverage() are now
just plot_gene_coverage() and ..plot_gene_coverage().

When method = 'broadenrich' only output the ..plot_gene_coverage()
plot. The other plots are not relevant.
Documentation changes and bumped package version

*Changes to and creation of R help files. Updated the vignette for the
package.
*Altered the NAMESPACE to recognize plot_gene_coverage.
*Updated DESCRIPTION to include multicore as enhancer package. Bumped
up version number in keeping with Bioconductor versioning guidelines
(as far as I understand).
*News summarizes changes to the package.
*Updated install_chipenrich.R file. Tested on Mac, Windows, and Linux.