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/sha256.h

@@ -0,0 +1,18 @@
+#ifndef NEOVIM_SHA256_H
+#define NEOVIM_SHA256_H
+
+typedef struct {
+  uint32_t total[2];
+  uint32_t state[8];
+  char_u buffer[64];
+} context_sha256_T;
+
+void sha256_start(context_sha256_T *ctx);
+void sha256_update(context_sha256_T *ctx, char_u *input, uint32_t length);
+void sha256_finish(context_sha256_T *ctx, char_u digest[32]);
+char_u *sha256_bytes(char_u *buf, int buf_len, char_u *salt, int salt_len);
+char_u *sha256_key(char_u *buf, char_u *salt, int salt_len);
+int sha256_self_test(void);
+void sha2_seed(char_u *header, int header_len, char_u *salt, int salt_len);
+
+#endif  // NEOVIM_SHA256_H