Improve method names in all classes of DataFrame-IO package

[olekscode]

Some names are very bad.
For example, uniform and uniformDefaultValue are booleans so they should be called something like isUniform and isUniformDefaultValue (although I'm not sure what that second one means).

What is orient?

defaultLineEndConvention should be defaultNewLineCharacter or something like that

... etc., etc., etc.

[DARK-art108]

@olekscode can you provide more explanation on what we are trying to achieve I have read the above issue comment but not able to understand it clearly.