javadoc improvements
Extract ErrorCollector to reuse it and avoid this error when using both SoftAssertions from core and the one generated by AssertJ generator

duplicate class definition for name: "org/assertj/core/api/AbstractAssert$$FastClassByCGLIB$$a3915617"
Add new contributor : Mariusz Smykula
Fixes #142 - assertThat(Iterator) javadoc should clearly state that the given iterator is consumed.