Adding .gitattributes (flutter#32)

This ensures correct line endings for commits from all platforms.

Author: goderbauer

.gitattributes

@@ -0,0 +1,25 @@
+# Auto detect text files and perform LF normalization
+*        text=auto
+
+# Always perform LF normalization on these files
+*.dart   text
+*.gradle text
+*.html   text
+*.java   text
+*.json   text
+*.md     text
+*.py     text
+*.sh     text
+*.txt    text
+*.xml    text
+*.yaml   text
+
+# Make sure that these Windows files always have CRLF line endings in checkout
+*.bat    text eol=crlf
+*.ps1    text eol=crlf
+
+# Never perform LF normalization on these files
+*.ico    binary
+*.jar    binary
+*.png    binary
+*.zip    binary