Provide boolean outputs that report on equality for certain conditions

[robne1982]

For examples:

• Do datasets match (all.equals but with our processing)
• Are all rows present
• Are all cols present
• Does data match
• etc

[robne1982]

Given the other bugs and slow progress, removing the v1.1.2 tag - we'll aim to come back to this later.

[robne1982]

Thinking about how this interacts with #23 (and this may be obvious) but these functions will need to interrogate the rCompare object, and therefore, if we fix #23, we should ensure we always produce a valid object.