Shorter multiple imports

[embar-]

Moving multiple imports from same sources into single call.
This should reduce DBML parse time more than twice.
See #59

[Vanderhoof]

Actually imports organization should not affect the performance. Separate-line imports was a design choice when I was beginning the project, not so sure about it right now, because IDEs like PyCharm manage imports pretty good for you and separate-line imports do not really make much sense at this point. But again, this is just code organization and should not be related to performance issues

[embar-]

Initially I also had similar thoughts. But actually I am using PyCharm, and indeed reorganization of imports did trick - code is 2-3 times faster. Maybe this is because importing not just functions, but also variable declarations multiple times that calls pp many times.

[Vanderhoof]

That's really strange! I just tried parsing the same file with and without collapsed imports, and saw no difference (86ms with one-line imports and 87ms with collapsed)

[embar-]

This time improvement was prior disabling unicode. Yes, it has practically no impact after disabling unicode.