Thanks everybody for advices, patience and support. I (proudly) announce version 0.3.1 (in extras-devel already).

There're a bunch of features to announce, among them (+ additions, - deletions, * fixes):

+ trigonometry and logarithm functions,
+ pi and e constants,
* fixed operations sorting algorithm to emulate infix operations correctly (modified shunting yard algorithm is used),
+ internationalization support (Russian and English locales are available for now),
+ two autoorientation modes: "Automatic (slider)" switches according slider position only, and "Automatic (accel)" uses accelerometer to set orientation,
+ autobase mode (according epage's advice, if I got him correctly at the end): the calculator's base is set to last base used to enter number.

And many other small tweaks and fixes.

I hope you'll like it!

Bugreports, advices and other feedback are wellcome as always.