expose SCTs in cleaner fashion

[machow]

We're doing this little song and dance right now.

from sqlwhat.checks.check_result import check_result, test_has_columns, test_nrows, test_ncols, test_column, allow_error, test_error, test_name_miscased, test_column_name
from sqlwhat.checks.check_logic import fail, multi, extend, test_or, test_correct
from sqlwhat.checks.check_funcs import check_node, check_field, test_student_typed, has_equal_ast, test_mc, success_msg, verify_ast_parses

Should be easier to just define a variable __all__ on each individual module

[filipsch]

I thinks it's beautiful ;) Very minor imo.

[machow]

The current form does have the advantage of making very clear where each SCT is coming from! We could always just have each import statement span multiple lines, rather than one super long one :p.