Create AtmelStudio.gitignore

Added a new .gitignore for Atmel Studio.
https://www.microchip.com/mplab/avr-support/atmel-studio-7

community/embedded/AtmelStudio.gitignore

+## Ignore Atmel Studio temporary files and build results
+# https://www.microchip.com/mplab/avr-support/atmel-studio-7
+
+# Atmel Studio is powered by an older version of Visual Studio,
+# so most of the project and solution files are the same as VS files,
+# only prefixed by an `at`.
+
+#Build Directories
+[Dd]ebug/
+[Rr]elease/
+
+#Build Results
+*.o
+*.d
+*.eep
+*.elf
+*.hex
+*.map
+*.srec
+
+#User Specific Files
+*.atsuo