Introduce nvim namespace: Move files.

Move files from src/ to src/nvim/.
- src/nvim/ becomes the new root dir for nvim executable sources.
- src/libnvim/ is planned to become root dir of the neovim library.

src/nvim/proto.h

@@ -0,0 +1,49 @@
+#ifndef NEOVIM_PROTO_H
+#define NEOVIM_PROTO_H
+
+/*
+ * VIM - Vi IMproved	by Bram Moolenaar
+ *
+ * Do ":help uganda"  in Vim to read copying and usage conditions.
+ * Do ":help credits" in Vim to see a list of people who contributed.
+ */
+
+/*
+ * proto.h: include the (automatically generated) function prototypes
+ */
+
+/*
+ * Don't include these while generating prototypes.  Prevents problems when
+ * files are missing.
+ */
+#if !defined(PROTO) && !defined(NOPROTO)
+
+/*
+ * Machine-dependent routines.
+ */
+/* avoid errors in function prototypes */
+#  define Display int
+#  define Widget int
+#  define GdkEvent int
+#  define GdkEventKey int
+#  define XImage int
+
+/* These prototypes cannot be produced automatically and conflict with
+ * the old-style prototypes in message.c. */
+int
+smsg(char_u *, ...);
+
+int
+smsg_attr(int, char_u *, ...);
+
+int
+vim_snprintf_add(char *, size_t, char *, ...);
+
+int
+vim_snprintf(char *, size_t, char *, ...);
+
+int vim_vsnprintf(char *str, size_t str_m, char *fmt, va_list ap, typval_T *tvs);
+
+#endif /* !PROTO && !NOPROTO */
+
+#endif  // NEOVIM_PROTO_H