Refactor code to not require Spring JDBC as mandatory dependency

[pull-vert]

spring-jdbc is now an optional dependency, wich is a good thing !
But this leads to an error

java.lang.NoClassDefFoundError: org/springframework/jdbc/core/SqlProvider
...
at org.springframework.data.r2dbc.function.DefaultSqlResult.<init>(DefaultSqlResult.java:78) ~[spring-data-r2dbc-1.0.0.BUILD-SNAPSHOT.jar:1.0.0.BUILD-SNAPSHOT]

In DefaultSqlResult, this line does not compile anymore, because SqlProvider is a spring-jdbc Interface

interface SqlFunction<T, R> extends Function<T, R>, SqlProvider {}

Workaround is to add dependency on spring-jdbc in my project, but the fix would be to not depend anymore on spring-jdbc 😄

Maybe there are other spring-jdbc remaining uses in r2dbc.

[mp911de]

Thanks for reporting the issue. We want to only provide optional features that build on Spring JDBC and we should not have mandatory dependencies in our code.

With the merge of #97 the left-over dependencies became visible.

[mp911de]

That's fixed now.