Remove unnecessary local variable
Unset the dataView object after all parsing is done

The dataView object stores a lot of the total memory used, especially if we
send in the whole image file. Since we don't need it after the parsing of the
data is done we can unset it to let it be garbage collected.
Add method for deleting a tag

This is mainly to be able to delete large tags. Also, add specific tip about
deleting the MakerNote tag since that one can be really large for some
manufacturers.
Add tip about and examples for only reading start of file

An image can be several megabytes in size but the Exif info will be at the
beginning of the file. Therefore we only need to read a small portion of the
image data. Add tip about this in the README file and update the examples with
how to do this.
Clean up code
Add installation notes for using Bower