feature: support for non upper case column name

[tnazare]

add DialectHelper to handle uppercase. For now it is very short but I think it can became an entry point to select dialect strategy.

Add a non-standard entry point keyword "using" in Assertions.

By default, assertj-db is still upper-casing every column name

See #32 #31

[regis1512]

I will try to see that tonight.
Thanks

[regis1512]

I saw that idea.
It is a good idea which make an answer in some cases.

But i think there are more case :

• the user can consider the name of tables, the name of columns and the name of primary keys
• he can want to compare the names with the case or ignore it
• he can want to have the name exactly like given by the metadata of the database or transform with upper or lower case

So to take more case, i have implemented new classes : LetterCase and all associated classes (especially SourceWithLetterCase and DataSourceWithLetterCase).

But thanks for your work, if there was not all these cases i will certainly take your solution.