Add alphabets: spanish, english and ascii

[jorgepiloto]

This PR partially solves for #2, since integrates some of the alphabets asked for in that issue. Further investigation on ASCII printable characters is needed and also in UTF-8 before including more alphabets 🐍

[codecov-io]

Codecov Report

Merging #5 into master will increase coverage by 21.56%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master       #5       +/-   ##
===========================================
+ Coverage   66.66%   88.23%   +21.56%     
===========================================
  Files           4        6        +2     
  Lines          12       34       +22     
  Branches        1        1               
===========================================
+ Hits            8       30       +22     
  Misses          4        4

Impacted Files	Coverage Δ
src/cipherkit/alphabets.py	100% <100%> (ø)
tests/test_alphabets.py	100% <100%> (ø)

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