Add base64 support

Lua Server Pages may now call the EncodeBase64() and DecodeBase64()
functions should they wish to do things like emit embeded data URIs

See #97

net/http/base64.h

@@ -0,0 +1,11 @@
+#ifndef COSMOPOLITAN_NET_HTTP_BASE64_H_
+#define COSMOPOLITAN_NET_HTTP_BASE64_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+char *EncodeBase64(const void *, size_t, size_t *);
+void *DecodeBase64(const char *, size_t, size_t *);
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_NET_HTTP_BASE64_H_ */