core/commands/unixfs: Rename 'ipfs unixfs' to 'ipfs file'

To be less confusing to newcomers (the IPFS filesystem isn't
Unix-specific anyway, and it isn't even very POSIX-specific [1,2,3]).
I'm a bit uncertain about having one name for users and another for
devs, but the consensus seems to be that mainaining two names is worth
the trouble [4].  We also kicked around:

* 'files' (plural),
* 'filesystem' (too long), and
* 'fs' (redundant after 'ipfs', even though IPFS isn't just about
  filesystems)

on IRC [5 through 6].  I wish there was a more evocative term.  I'm
never sure where "file" lands on the scale between "filesysytem",
"everything is a file", "a single chunk of data with an associated
inode".  But we can't think of anything better.

[1]: https://github.com/ipfs/go-ipfs/pull/1348#issuecomment-110529070
[2]: https://github.com/ipfs/go-ipfs/pull/1348#issuecomment-110529921
[3]: https://github.com/ipfs/go-ipfs/pull/1136/files#r29377283
  In my response to this (no longer visibile on GitHub):

  On Wed, Apr 29, 2015 at 01:30:04PM -0700, Juan Batiz-Benet wrote:
  > > +package fsnode
  >
  > i think this package should be called `unixfs` as that's the
  > abstraction that this is calling to.

  Will do, although I don't see what's especially Unix-y about these
  file nodes.

[4]: https://github.com/ipfs/go-ipfs/pull/1348#issuecomment-110529811
[5]: https://botbot.me/freenode/ipfs/2015-06-09/?msg=41428456&page=5
[6]: https://botbot.me/freenode/ipfs/2015-06-09/?msg=41430703&page=5

License: MIT
Signed-off-by: W. Trevor King <wking@tremily.us>

core/commands/root.go

@@ -36,7 +36,7 @@ DATA STRUCTURE COMMANDS
 
     block         Interact with raw blocks in the datastore
     object        Interact with raw dag nodes
-    unixfs        Interact with Unix filesystem objects
+    file          Interact with Unix filesystem objects
 
 ADVANCED COMMANDS
 
@@ -104,7 +104,7 @@ var rootSubcommands = map[string]*cmds.Command{
 	"stats":     StatsCmd,
 	"swarm":     SwarmCmd,
 	"tour":      tourCmd,
-	"unixfs":    unixfs.UnixFSCmd,
+	"file":      unixfs.UnixFSCmd,
 	"update":    UpdateCmd,
 	"version":   VersionCmd,
 	"bitswap":   BitswapCmd,