Build a function with two input arguments: a string and a word length (number of letters), that outputs a vector of counts of the 26 letters of the alphabet, specific to words with a given length.

• Case insensitive.
• Words contain only letters a-zA-Z, but the string can contain punctuation.

Example

 >> txt = 'Hello World, from MATLAB' ;
 >> nl  = 5 ;                              % Number of letters.
 >> nlWords_getCounts(txt, nl)
 ans = 
     0  0  0  1  1  0  0  1  0  0  0  3  0  0  2  0  0  1  0  0  0  0  1  0  0  0

here, two 5 letters words are found: 'Hello' and 'World'. The output vector is the count of letters (1 to 26) in these two words taken together. For example, letter 12 is 'l/L' and we see that it appears 3 times, hence the count of 3.