Add a feature to analyse word frequencies

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Telaro should be able to analyse a text for word frequencies:

$ ./telaro.py --word-frequencies --training-text drsuess.txt;

Word frequencies in file "drsuess.txt":

the 1203
on  625
sat 340
mat 289
cat 150
...
$

This should be subsettable by an input string. If subset, Telaro should 
output on STDERR the characters needed to typeset the document:


$ ./telaro.py --input-characters atmc --word-frequencies --training-text 
drsuess.txt;

Warning: File "drsuess.txt" needs these characters to be typeset:

d e h i j k l o s x z

mat 289
cat 150
mac 15
....
$

Original issue reported on code.google.com by d.crossland on 25 May 2010 at 11:44