Accept entries starting with ? as ignored

Because it makes much sense and it is a lot quicker to add a ? at the beginning of the line if it is already written !
fix the last commit to use a correct Python syntax
throw a ParseError when the user enters an out of bound time
fix date formatting when no encoding is set (eg. in tests)
fix editor invocation when its path contains a space (fixes #17)
automatically select unique choice in add command (fixes #19)
report error when using the -xx time notation for an alias that doesn't exist (fixes #20)
make the start command use the end time of the previous entry if any (fixes #21)
fix start command on empty date (fixes #21)
issue #18 WIP rewrite start time of non-pushed entries
rewrite start time of non-pushed entries (fixes #18)
Merge remote-tracking branch 'origin/issue_18'
add missing import of ConfigParser
issue #22: add support for shared aliases
use setuptools instead of distutils
add shared aliases information upon taxi update
improve output for overlapping/added aliases
Merge remote-tracking branch 'origin/shared_aliases'
bump version number to 3.1.0
remove incorrect alias in sample tksrc file