[doc] Fix some typos and add some links
Added "clean" rule to examples/Makefile
Remove BerkeleyDB from doc and INSTALL (--enable-bdb)
Use AM_SILENT_RULES when building
Update .gitignore
Merge pull request #22 from PabloCastellano/master

Documentation and minor improvements
Merge branch 'master' of https://github.com/spesmilo/libbitcoin