Added sanity check for compiling example

.travis.yml

@@ -1,4 +1,14 @@
 script:
+    # make sure example can at least compile
+    - sed -n '/``` c/,/```/{/```/d; p;}' README.md > test.c &&
+      CFLAGS='
+        -Duser_provided_block_device_read=NULL
+        -Duser_provided_block_device_prog=NULL
+        -Duser_provided_block_device_erase=NULL
+        -Duser_provided_block_device_sync=NULL
+        -include stdio.h -Werror' make
+
+    # run tests
     - CFLAGS="-DLFS_READ_SIZE=16  -DLFS_PROG_SIZE=16"  make test
     - CFLAGS="-DLFS_READ_SIZE=1   -DLFS_PROG_SIZE=1"   make test
     - CFLAGS="-DLFS_READ_SIZE=512 -DLFS_PROG_SIZE=512" make test

README.md

@@ -77,7 +77,6 @@ int main(void) {
 
     // update boot count
     boot_count += 1;
-    printf("boot_count: %ld\n", boot_count);
     lfs_file_rewind(&lfs, &file);
     lfs_file_write(&lfs, &file, &boot_count, sizeof(boot_count));
 
@@ -86,6 +85,9 @@ int main(void) {
 
     // release any resources we were using
     lfs_unmount(&lfs);
+
+    // print the boot count
+    printf("boot_count: %d\n", boot_count);
 }
 ```