help: pass subtopic into help() Now that we have multiple directories where help topics can live, we need a mechanism to access them. We already use "." to separate topic from section. So it seems logical to also use "." to denote the sub-directory of a topic. This patch teaches the help command to parse out the possible sub-topic and pass it to the help system.

help: add "internals" topic We introduce the "internals" help topic, which renders an index of available sub-topics. The sub-topics themselves are still not reachable via the help system.

help: teach loaddoc to load from a different directory The help system currently only supports showing help topics from a single directory. We'll need to teach it to show results from different directories in order to show the internals topics. The first step is to teach loaddoc() to load documentation from a sub-directory.

setup.py: package internals help files mpm says internal docs should be visible via `hg help` and hgweb. They need to be in the distribution for this to work. Package them.

help: add documentation for bundle types Bundle types and the high-level data format of each bundle isn't documented anywhere. Let's document this as well. Obviously there are many more details about bundles that could be written about. But you have to start somewhere.

help: add documentation for changegroup formats There is no formal location for spec-like technical/internal docs. The repository makes sense as such a location because spec-like documentation should be reviewed (ruling out a wiki). mpm has also stated that he would like this documentation to be part of the built-in help system. So, we establish an "internals" sub-directory to hold this class of documentation. The format of changegroups does not appear to be documented anywhere, even in source code. It therefore seemed like an appropriate first thing to document. This patch adds low-level documentation of versions 1 and 2 of the changegroup foromat. It currently only describes the raw data format. There is probably room to write higher-level documentation on strategies for producing and consuming the data. We'll leave that for another day. The added file is not yet accessible via `hg help` nor via hgweb. Support for this will follow in subsequent patches.