Update documentation

[montesmariana]

I went through the communication of the package and made the changes we agreed on:

• iget() and ireadRDS() are documented together.
• iput() and isaveRDS() are documented together.
• irm() and imkdir() have been separated.
• imeta() and iquery() have been separated.
• icd(), ipwd() and ils() have been partially updated - I will finish that once the latest fixes arrive.

Next to splitting and sometimes rephrasing the documentation, I also made the following changes:

• in irm(), the unregistered argument (which was not implemented) was removed, and the trash argument was renamed to force so that the behavior is more clear and matches iCommands: force = TRUE deletes permanently, whereas force = FALSE sends to trash.
• in imeta() and iquery() I changed some arguments to have specific options with the first one being the default

Finally, I added comments for two changes that will come soon:

• In imeta(), operations will be a list of named lists/vectors (which actually already works, but needs better validation)
• imkdir() can also be split into itouch() and imkdir(), so the function will become an internal function called by those two. I didn't implement that yet so I can write proper tests.

[MartinSchobben]

As discussed before, I agree with these changes. @trel can you merge this, if you agree with it.

[trel]

of course. merging!