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/log.h

@@ -0,0 +1,57 @@
+#ifndef NEOVIM_LOG_H
+#define NEOVIM_LOG_H
+
+#include <stdbool.h>
+
+#include "func_attr.h"
+
+#define DEBUG_LOG_LEVEL 0
+#define INFO_LOG_LEVEL 1
+#define WARNING_LOG_LEVEL 2
+#define ERROR_LOG_LEVEL 3
+
+bool do_log(int log_level, const char *func_name, int line_num,
+            const char* fmt, ...) FUNC_ATTR_UNUSED;
+
+#define DLOG(...)
+#define ILOG(...)
+#define WLOG(...)
+#define ELOG(...)
+
+// Logging is disabled if NDEBUG or DISABLE_LOG is defined.
+#ifdef NDEBUG
+#  define DISABLE_LOG
+#endif
+
+// MIN_LOG_LEVEL can be defined during compilation to adjust the desired level
+// of logging. DEBUG_LOG_LEVEL is used by default.
+#ifndef MIN_LOG_LEVEL
+#  define MIN_LOG_LEVEL DEBUG_LOG_LEVEL
+#endif
+
+#ifndef DISABLE_LOG
+
+#  if MIN_LOG_LEVEL <= DEBUG_LOG_LEVEL
+#    undef DLOG
+#    define DLOG(...) do_log(DEBUG_LOG_LEVEL, __func__, __LINE__, __VA_ARGS__)
+#  endif
+
+#  if MIN_LOG_LEVEL <= INFO_LOG_LEVEL
+#    undef ILOG
+#    define ILOG(...) do_log(INFO_LOG_LEVEL, __func__, __LINE__, __VA_ARGS__)
+#  endif
+
+#  if MIN_LOG_LEVEL <= WARNING_LOG_LEVEL
+#    undef WLOG
+#    define WLOG(...) do_log(WARNING_LOG_LEVEL, __func__, __LINE__, __VA_ARGS__)
+#  endif
+
+#  if MIN_LOG_LEVEL <= ERROR_LOG_LEVEL
+#    undef ELOG
+#    define ELOG(...) do_log(ERROR_LOG_LEVEL, __func__, __LINE__, __VA_ARGS__)
+#  endif
+
+#endif
+
+#endif  // NEOVIM_LOG_H
+