Cleanup and fixup

Non-stylistic changes:
  * Add LuaDoc/LDoc support.  Generate API documentation with `ldoc .`. (see screenshots below)
  * Fix `clear_objects` area size calculation.
  * Fix `clear_objects` removing player objects.
  * Fix shadowing of marker entity name with player name.  (this broke `clear_objects` in yet another way)
  * Make visualization functions use `swap_node`.
  * Make hidden nodes unwalkable.
  * Prevent `hide` from hiding air.
  * Make deprecated functions log to deprecated stream when called.
  * Fixed `we-replaceinverse` not using normalized node names.
  * Added .gitignore (Just `*~` for now).
  * Bump version to 1.1.

Stylistic changes:
  * Change `x = function` to `function x`.
  * Change comment format. ("--foo" -> "-- Foo")
  * Make  missing VoxelManip error less obnoxious.
  * Move `sort_pos` into `common.lua`, which is a required module (it was already copied about three times, and it needed to be copied again for a module that was missing it, there's not really a reason to exclude it too, so requiring it is O.K.).
  * Remove local copies of `minetest`.  (Anything that used a core function in a speed-critical area localized the specific function needed, so the speedup was minimal)
  * Remove `worldedit = worldedit or {}` from modules. (`init.lua` defines this)
  * Replace replaceinverse with an inverse argument to `replace`.
  * Added `error()`s on on invalid axes.
  * Change `wip` to `TODO`.
  * Rename `clearobjects` to `clear_objects`.
  * Remove `hollow_{sphere,dome,cylinder}` and replace them with a hollow parameter to each function.
  * Add helpers to reduce code duplication.
  * Renamed `Chat Commands.md` to `ChatCommands.md` (LDoc has an issue with the space).

Generated documentation (this is a little outdated, but it's mostly the same):
![WorldEdit documentation index](https://cloud.githubusercontent.com/assets/3399154/4837919/37d0eb90-5fe0-11e4-981a-f81079512be4.png)
![WorldEdit documentation detail for stretch](https://cloud.githubusercontent.com/assets/3399154/4837921/3e3e6386-5fe0-11e4-863f-2116ce2c2ce3.png)
Note: Due to the number of changes it's hard to thoroughly test this, so I wouldn't be surprised if this introduces a few bugs.