GitHub actions (#2)

* Updated readme, enabled automatc testing

* Snapshot support

* Release CI support

Co-authored-by: Salomon BRYS <salomon@kodein.net>

jni/build.sh

@@ -15,6 +15,7 @@ JNI_HEADERS=$TARGET
 if [ "$TARGET" == "linux" ]; then
   OUTFILE=libsecp256k1-jni.so
   ADD_LIB=-lgmp
+  CC_OPTS="-fPIC"
 elif [ "$TARGET" == "darwin" ]; then
   OUTFILE=libsecp256k1-jni.dylib
   if [ -z "$CROSS_TRIPLE" ]; then
@@ -24,7 +25,7 @@ elif [ "$TARGET" == "mingw" ]; then
   OUTFILE=secp256k1-jni.dll
   CC=/usr/src/mxe/usr/bin/x86_64-w64-mingw32.static-gcc
   JNI_HEADERS=linux
-  CC_OPTS="-fpic"
+  CC_OPTS="-fPIC"
 fi
 
 mkdir -p build/jni/$TARGET