+- `common.h` is gone. Everything useful in it was moved to `ircd_defs.h`.
+- `config.h` is gone; the few remaining knobs in it were not for configuration
+ by mere mortals, and mostly existed as a 2.8 relic. Most of the knobs live in
+ `defaults.h`, but one is well-advised to stay away unless they know exactly
+ what they are doing.
+- A new module API has been introduced, known as AV2. It includes things such as
+ module datecodes (to ensure modules don't fall out of sync with the code),
+ module descriptions, and other fun things.
+- Alias and module commands are now in m_alias and m_modules, respectively, and
+ can be reloaded if need be. For sanity reasons, m_modules is a core module,
+ and cannot be unloaded.
+- irc_dictionary and irc_radixtree related functions are now in librb, and
+ prefixed accordingly. Typedefs have been added for consistency with existing
+ data structures. For example, now you would write `rb_dictionary *foo` and
+ `RB_DICTIONARY_FOREACH`.
+- C99 bools are now included and used in the code. Don't use ints as simple true
+ or false flags anymore. In accordance with this change, the `YES`/`NO` and
+ `TRUE`/`FALSE` macros have been removed.
+- Return types from command handlers have been axed, as they have been useless
+ for years.
+- libratbox has been renamed to librb, as we have diverged from upstream long
+ ago.