Add a section header for plugins.

Adds a section header for plugins so people can link directly to this section.
Merge pull request #225 from wilmoore/patch-1

Add a section header for plugins.
support require('..'). closes: #231
Merge pull request #233 from duojs/fix/231

support require('..'). closes: #231
Safer way to check if a path is a file

Directories can contain `.` too.
Fixed path root checking in findroot()
Fixed npm warn for missing repository field on package.json
Merge pull request #242 from ruyadorno/fix-npm-repository-warn

Fixes a npm warning
Merge pull request #216 from kevva/is-file

Safer way to check if a path is a file
Use path.sep when splitting cwd.
Merge pull request #241 from darsain/fix/findroot

Fixed hanging on windows when there is no manifest