Add trivial fuzzer for parser

As described in #61, fuzz testing some parts of this would be ~~fun~~
helpful. So, I started with the most trivial fuzzer I could think of:
Put random stuff into File::parse and see what happens.

To speed things up, I also did

    cp src/**/*.rs fuzz/corpus/parser/

in the `crates/libsyntax2/` directory (running the fuzzer once will
generate the necessary directories).

1 files changed, 4 insertions, 0 deletions

diff --git a/crates/libsyntax2/fuzz/.gitignore b/crates/libsyntax2/fuzz/.gitignore
new file mode 100644
index 000000000..572e03bdf
--- /dev/null
+++ b/crates/libsyntax2/fuzz/.gitignore
@@ -0,0 +1,4 @@
+
+target
+corpus
+artifacts