Add ability to subscribe to table updates.

This was implemented based on
[this](https://www.sqlite.org/c3ref/update_hook.html) document.

src/esqlite3.erl

@@ -22,6 +22,7 @@
 
 %% higher-level export
 -export([open/1, open/2,
+         set_update_hook/2, set_update_hook/3,
          exec/2, exec/3,
          changes/1, changes/2,
          insert/2,
@@ -69,6 +70,22 @@ open(Filename, Timeout) ->
             Error
     end.
 
+%% @doc Subscribe to database notifications
+%% Messages will come in the shape {action, table, id}
+%% Where action will be insert | update | delete
+%% and table will be a string
+%% and id will be an integer
+%%
+-spec set_update_hook(pid(), connection()) -> ok | {error, term()}.
+set_update_hook(Pid, Connection) ->
+    set_update_hook(Pid, Connection, ?DEFAULT_TIMEOUT).
+
+-spec set_update_hook(pid(), connection(), timeout()) -> ok | {error, term()}.
+set_update_hook(Pid, {connection, _Ref, Connection}, Timeout) ->
+    Ref = make_ref(),
+    ok = esqlite3_nif:set_update_hook(Connection, Ref, self(), Pid),
+    receive_answer(Ref, Timeout).
+
 %% @doc Execute a sql statement, returns a list with tuples.
 -spec q(sql(), connection()) -> list(tuple()) | {error, term()}.
 q(Sql, Connection) ->
@@ -208,7 +225,7 @@ fetchall_internal(Statement, ChunkSize, Rest) ->
 
 %% Try a number of steps, when the database is busy,
 %% return rows in revers order
--spec try_multi_step(statement(), pos_integer(), list(tuple()), non_neg_integer()) -> 
+-spec try_multi_step(statement(), pos_integer(), list(tuple()), non_neg_integer()) ->
                 {rows, list(tuple())} |
                 {'$done', list(tuple())} |
                 {error, term()}.

src/esqlite3_nif.erl

@@ -23,6 +23,7 @@
 %% low-level exports
 -export([start/0,
          open/4,
+         set_update_hook/4,
          exec/4,
          changes/3,
          insert/4,
@@ -62,6 +63,9 @@ start() ->
 open(_Db, _Ref, _Dest, _Filename) ->
     erlang:nif_error(nif_library_not_loaded).
 
+set_update_hook(_Db, _Ref, _Dest, _Pid) ->
+    erlang:nif_error(nif_library_not_loaded).
+
 %% @doc Exec the query.
 %%
 %% Sends an asynchronous exec command over the connection and returns