Add Bluepill example & some other minor improvements (#28)

- added bluepill example
- improved ci config
- travis: run fmt only once
- travis: fixed target issues

examples/epd4in2_full_blue_pill/.cargo/config

@@ -0,0 +1,12 @@
+[target.thumbv7m-none-eabi]
+
+# uncomment ONE of these three option to make `cargo run` start a GDB session
+# which option to pick depends on your system
+runner = "arm-none-eabi-gdb -q -x openocd.gdb"
+# runner = "gdb-multiarch -q -x openocd.gdb"
+# runner = "gdb -q -x openocd.gdb"
+
+rustflags = ["-C", "link-arg=-Tlink.x"]
+
+[build]
+target = "thumbv7m-none-eabi"