I develop larger projects like libraries using an external text editor to which I am already very accustomed, editing the library files directly in the libraries/bitlash/src directory (for example). Then I switch to the Arduino IDE, where I have opened an example sketch which includes the library (for an example see bitlashdemo), to recompile and upload.
You might call it the Alt+Tab/Alt+U IDE. Anyway, it works for me. I will need a new Alt key soon, though.
-br
PS: Should have mentioned that to protect against my own confusion I also have a terminal window open so I can commit changes to git every so often and push them somewhere safe several times per day.