Add event flog

I needed this, and it should be there.

[ci skip]

src/event.cpp

@@ -265,6 +265,7 @@ static void event_fire_internal(parser_t &parser, const event_t &event) {
         scoped_push<bool> interactive{&ld.is_interactive, false};
         auto prev_statuses = parser.get_last_statuses();
 
+        FLOGF(event, L"Firing event '%ls'", event.desc.str_param1.c_str());
         block_t *b = parser.push_block(block_t::event_block(event));
         parser.eval(buffer, io_chain_t());
         parser.pop_block(b);

src/flog.h

@@ -56,6 +56,8 @@ class category_list_t {
 
     category_t config{L"config", L"Finding and reading configuration"};
 
+    category_t event{L"event", L"Firing events"};
+
     category_t exec_job_status{L"exec-job-status", L"Jobs changing status"};
 
     category_t exec_job_exec{L"exec-job-exec", L"Jobs being executed"};