If you use that there will be no actual library available and everything must be done by direct access to registers using your own code and through readings of the manual. This can be the most laborious route for your purpose, but it will result in the smallest code size.
This is how I do most of my work, and it's a lot less work than people seem to think. The best part is I only need ONE document open (the reference manual), and I can code straight from that, because the register and bit field names in the CMSIS headers follow the reference manual exactly, with very few exceptions. When I am forced to use a library I am constantly hunting around for the right constants and function names; this wastes a lot of time and is no fun at all. Obviously, writing your own drivers is more work in some sense, but if you stick with a family like STM32 you very quickly get to the point where you are just copy/pasting from previous projects with small modifications.
If that's the way you like to work you *really* should look at Mecrisp-Stellaris
http://mecrisp.sourceforge.net/Matthias Koch has done a brilliant job in the implementation, The great beauty of forth is the language is the operating system and the editor. All you need is a dumb terminal window on a PC and a USB-serial adaptor with 3.3 V Tx & Rx lines.
There are over 30 ARM based boards it runs on, so it's almost certain you have a board that has a prebuilt image. The following list is *just* the STM32 based ARM ports.
STM L053 Discovery STM32L053C8T6
STM Nucleo L152RE STM32L152RE
STM Nucleo F207ZG STM32F207ZG
STM Nucleo F303K8 STM32F303K8
STM Nucleo 401RE STM32F401RE
STM Nucleo 411RE STM32F411RET6
STM F0 Discovery STM32F051R8
STM VL Discovery STM32F100RB
Shenzhen LC Technology board STM32F103C8T6 (aka the blue pill)
STM F3 Discovery STM32F303VCT6
STM F4 Discovery STM32F407VGT6
STM F429 Discovery STM32F429ZIT6
Very small TSSOP20 packaged STM32F030F4
STM L152 Discovery STM32L152RBT6
STM L476 Discovery STM32L476VG
STM F746 Discovery STM32F746NG
Terry Porter has been building a very nice documentation site for Mecrisp.
http://hightechdoc.net/mecrisp-stellaris/_build/html/index.htmlForth is a very different mind set from assembly or C. But once you understand the philosophy and how the outer interpreter works it's very intuitive. If you're an HP calculator fan you'll feel right at home as it is RPN.
FWIW the STM32F030F4 has 16 KB of flash and 4 KB of SRAM. That's about the size of the machine Chuck Moore developed forth on, except it's a much faster clock rate.