Alignment not validated when set for specific field

[myheroyuki]

What did you do?

Attempted to set the alignment for a header field to the invalid alignment value "rice".

What did you expect to happen?

ValueError: Alignment rice is invalid, use l, c or r. This is what happens when the alignment is set globally and not just for a single field.

What actually happened?

No error message, and the table printed out with the default alignment. If I try to print a formatted html table it crashes with a key error.
It seems like the setter where the value is validated isn't called when assigning a key a value in the align dict.

Please include code that reproduces the issue.

The best reproductions
are
self-contained scripts
with minimal dependencies.

t = helper_table(rows=3)
t.format = True
t.align["Field 1"] = "rice"
print(t.get_string())

This is another small alignment issue I found looking into other alignment related issues like #199, #102 and #111