Add a common place where components can write messages to. Any
userinterface can decide, what messages should be visible
(depending on their severity).

Use multiples of 4 as indent, shorten overlong lines and fix
other minor things to keep pep8-conformity.

Move the calculations out of the `pre_check()` function.
Also do smarter checks:
  - If len(sequence) == 1, we don't need any rolls. In this case, just
    return sequence[0]
  - If len(sequence) is a factor of dice_sides, we only need one roll
    along with the modulo operator.
  - For everything else, just require one extra roll, bringing it to a
    total of 2 rolls. This should remove a little bit of the edge bias
    introduced by the modulo
Run the `pre_check()` function after the calculations have been done.

For the unit tests:
  - remove the function `test_choice_len_too_short()`;
    we no longer have to raise an exception when the sequence length is
    too short.
  - Write new tests for the cases where `dice_sides = 6` and `len(sequence)`:
     - 1
     - 2,3
     - 4,5

It is passing and doing as expected.

Use `.asc` filename extension for signed wordlists.

The original diceware list (with 7776 words) is still shipped with our
package.

also updated README

Fixes #16

Normally, it would be more concise to use the more declarative name.
"en_8k" tells, how many terms we find in this wordlist. But as the
wordlist names are used in the CLI and users will normally simply
look for a wordlist in their language, it can help to keep the name
of the "default" list for each language short.

We pick the 8K lists for "default" (and not the "original" 6^5
lists), because we assume that normally people will use diceware
without dice. Also most other sources of randomness will most
probably work on a 2^x basis rather than in 6^x (and therefore
have better use for 8k lists over other ones).

Make sure that config file values are really considered by
handle_options().

With the new config module in place we must make sure, that any user
maintained .diceware.ini files do not interfere with tests.

The fixture sets $HOME for all tests automatically.

This test name was a duplicate, in effect overwriting the other test.

We also have to check the "True" case to make the test relevant.

We have to check for boolean before int, because int is also
a valid boolean.

By default we should read config files in user
homes.

We can build a sensible list of config file locations on-the-fly.

Right now we consider a file ".diceware" in the users home as
only valid place for a diceware config file.

when looking for valid wordlists.

Only return path if it exists and is valid.

Activates the -w option. Turns out we still have to fix
`get_wordlist_path` at it assumes that wordlists all end in
``.txt`` (which is not true).

We have to try hard to create a string accepted by all supported
Python versions.

Add test case that provides a file descriptor with broken seek(). We
must expect "broken" seek() methods for instance with sys.stdin.