Do final alignment based on presence of <,>,^,0= in format string

Beginning to finalize the table-column alignment options for pprint in Table package.
You can improve speed by taking the `if elif .. else` outside the `for i, col_str .. ` loop, like:
```
import string
if '<' in format_:
    justify = string.ljust
elif '^' in format_:
    justify = string.center
...

for i, col_str in enumerate(col_strs):
    col_strs[i] = justify(col_str, col_width)
```
You can compare this in speed to the even more compact version using a list comprehension:
```
col_strs = [justify(col_str, col_width) for col_str in col_strs]
```