add dependencies status badge

Add badge to see if dependencies are up to date
Merge pull request #129 from podviaznikov/patch-1

add dependencies status badge
Update README.md and README.next.md to be closer to each other
Issue #131 - add documented `lint` function for use by editors/IDEs

It returns a map with data about warnings, rather than formatted
strings that combine everything and require parsing to split it up.
Fix #130 - add keywords :all, :default to options for specifying linters
Updates changes.md with changes in version 0.2.1
Fixup to previous commit
One more enhancement added to list of changes
Remove now-older copy of lint fn in doc/lint.clj with ref to where it is now
Fixing up future plans in changes.md
Change all versions to 0.2.1 in preparation for tagging and release
Try out Clojars Markdown code snippet to see what it looks like
Revert previous commit.  Didn't look good inside paragraph text
Change versions to 0.2.2-SNAPSHOT for further development
Update link for squiggly-clojure project
Update to match README
Correction to some debug code
A first draft implementation of new linter wrong-pre-post

I want to check it in as it is now, since it seems useful.  However, I
also want to experiment with changing its implementation
significantly, using tools.analyzer(.jvm) to get more information
about preconditions or postconditions that are symbols, to know
whether they are local symbols or Vars.
Rework :wrong-pre-post linter to tell locals from globals in conditions
Fix typo in link