Bugfixes and speedups

• Add instructions for using with plugin managers.
• Fix the command line string formatting problems.
• Make dutyl#core#bytePosition always use unix file format.
• Fix usage for Windows without VimProc.
• Support both dub.json and package.json as the DUB file.
• Change the DCD server control functions to use call instead of echo.
• Use DUB's --annotate flag to prevent downloading dependencies.
• Register import paths immediately when starting the DCD server.
• Clean import paths from last character if it's a path separator.