Fuzzing setup and fixes (#755)

* encode: fix localdate formatting
* encode: fix empty key marshaling
* encode: fix invalid quotation of time.Time
* encode: ensure control chars are escaped
* decode: always use UTC for zero tz
* encode: check for invalid characters in keys
* encode: always construct map for empty array tables
* fuzz: add go 1.18 fuzz test
* encode: handle NaNs
* encode: allow new lines in quoted keys
* encode: never emit table inside array
* encode: don't capitalize inf

.gitattributes

@@ -1,3 +1,4 @@
 * text=auto
 
 benchmark/benchmark.toml text eol=lf
+testdata/** text eol=lf