Use simpler method for computing letter from number

[livecodeali]

Use a simpler method for computing the uppercase letter corresponding to a given number between 1 and 26

[livecodeali]

This does not wrap around correctly. For example shifting U by 6 will cause fromNumber(27) to be called, which gives 64, (@ in ascii).

[livecodeali]

From the test log:

not ok - abjurer <-> nowhere (13)
# abjurer <-> nowhere (13) failed
# Expected result: nowhere
# Actual result: NOWGDRD

not ok - fusion <-> layout (6)
# fusion <-> layout (6) failed
# Expected result: layout
# Actual result: L@YOUT

not ok - manful <-> thumbs (7)
# manful <-> thumbs (7) failed
# Expected result: thumbs
# Actual result: THUMAS

Notice the letters that are shifted past Z and wrap around are all out by one.