8.1.0

Changes from previous version:
Fixes

• Fixed typo of class name PexepctMixin, replaced by PexpectMixin
  (57452bd). Backward compatibility layer implemented in 7eafbb3.
• Fixed undefined sh shell and set to bash (3c3f59b).
• Default implementation for the __init__ of Concern (de26777).

Enhancements

• Allow to change the shell with some predefined options: bash, dash,
  ksh (3c3f59b) with the new +shell option.
• Add better logs for the initial phases of byexample: modules load
  and parsing options (b6b371c, part of issue #66 ).
• Experimental Conditional Execution (a module) to allow to skip
  or not an example based on a condition (797052f). Introduces
  the +if, +on and +unless options.
• Restricted the set of possible characters for a tag name to letters,
  numbers, minus and dot symbols; the names must starts with a letter or a
  dot (a5707d4). The : symbol is allowed too but reserved for future
  uses. Related to issue #32 .
• Auto hide the non-printable replacement in the enhanced diff
  (ec24b30), closes #58.
• Warn about non-printable char replaced that could be confused
  (add2a0b), closes #30.
• Improved how the diff are shown (ec24b30, add2a0b).
• Allow call external diff program (c210b5b). Enable this with
  --diff tool and set the diff command line with --difftool <cmd>.
  Closes #20.

Documentation:

• More notes about checks (5bd91a0).
• FAQs (8028bb4, a5707d4)

Potential incompatible changes (examples)

• In Debian/Ubuntu based distros, sh is a symlink to dash. In
  byexample 8.1.0, sh is replaced by bash which it could break
  some examples. See the comments in 3c3f59b for a full explanation.
  In any case the incompatible changes should be easy to fix and if not,
  the user can force to rollback to dash with the option +shell=dash.
  For Red Hat/Fedora based distros, sh is a symlink to bash so
  it should be ok.