CHANGELOG: update all info from v1.0 to upcoming v1.1.0
README.md: update info for upcoming realease v1.1.0
AvailableBooksChecker: rename variables and beautify output
DownloadChecker: beautify output
.gitignore: add books list on repo top level, too
Add options '-c|--check-avail' and '-m|--check-md5'

Because Maven packages the application into a One-JAR, it is only
possible to use the main class (OpenbookCleaner) from outside, as tests
have shown. Thus, we need CLI options to dispatch to the main methods of
AvailableBooksChecker and DownloadChecker, respectively. If present, the
options will cause both helper classes to be executed in this order, but
always before OpenbookCleaner. So theoretically, users can run the
application in all three modes at once: the two diagnostic ones and the
normal book clean-up mode. Strange, but possible.
Avoid "you must specify at least one book ID" for '-m' and '-c' modes
CHANGELOG: add info about '-c|--check-avail', '-m|--check-md5' switches
README.md: add info about '-c|--check-avail', '-m|--check-md5' switches
README.md: add link to CHANGELOG, prepare for 1.1.0 release
pom.xml: prepare for 1.1.0 release