Create letter_statistic.py

a:68582
b:17798
c:34287
d:34552
e:106758
f:12714
g:27848
h:20200
i:77412

j:1780
k:9370
l:47011
m:24741
n:60513
o:54542
p:25789
q:1632
r:64965

s:86547
t:57059
u:31161
v:9186
w:8535
x:2700
y:13473
z:3750