Allow attribute transformations in SELECT clause

[khageshpatel]

Implements transformation on attributes. Currently only implements format(size,'kb'/'mb'/'gb'), upper, fullpath but other functions can easily be added. Example query:

fsql "select format(size,'kb'), upper(fullpath(name)) from ."

[kashav]

For #17.

[kashav]

I've tested this and it works pretty well; some minor problems (like mode being empty), but no worries, will add a full review in the next day or so.

I'm going to play around with the code and see if I can add support for WHERE attributes as well as clean-up the logic a little bit.

[kashav]

An update on this:

I thought it'd be a better idea to build this against the new parser structure (introduced in feature/subquery), so I've made some changes and pushed those to feature/attribute-modifiers.

I plan to work on this feature in that branch. Feel free to submit more work to that branch, should you have anything to add!

[khageshpatel]

@kshvmdn Thanks

[kashav]

Merged in 09ea293, thanks @khageshpatel!