Solarized colorscheme added.
fix crash in sha encode of previews

When opening certain filetypes, for which Ranger can't render a preview
(they appear as 0 bytes), Ranger will crash on the sha1_encode:

    Traceback (most recent call last):
    File "~/ranger/ranger/core/main.py", line 139, in main
        cacheimg = os.path.join(ranger.CACHEDIR, self.sha1_encode(path))
    File "~/ranger/ranger/core/actions.py", line 821, in sha1_encode
        sha1(path.encode('utf-8')).hexdigest()) + '.jpg'
    AttributeError: 'NoneType' object has no attribute 'encode'

This solves that by checking at the beginning of get_preview() that
`file.realpath` is not None, and returning early if it is None.
rename README to README.md

This way, github treats the README as a markdown file and displays it
nicely.
optimized README.md for github
config/rc.conf: don't use the obsolete -d flag
Added renameConsole a command which automatically creates a console for the rename command and places the cursor before the file extension.
Mapped renameConsole to 'A'
Fixed renameConsole usage in documentation.
Restored original rename mapping and added renameConsole under 'a'.
fix references to README.md
added dwb to the list of browsers
fix sorting by size in some corner case

see https://savannah.nongnu.org/bugs/index.php?42736
change the bug tracker URL
container.directory: implemented random sorting
Commands "yp", "yd", "yn" now copy to X11 clipboard selection too.
Added redrawing when we return to Vim from Ranger without opening any
file.
pressing <CR> directly after scout -ek doesn't delete the complete
console line anymore
New show_selection_in_titlebar setting
added doc/release-checklist.txt
added doc/ranger.1.html to .gitignore