describe: add example
tree-cache: correct the entry_count calculation

The entry_count field is the amount of index entries covered by a
particular cache entry, that is how many files are there (recursively)
under a particular directory.

The current code that attemps to do this is severely defincient and is
trying to count the amount of children, which always comes up to zero.

We don't even need to recount, since we have the information during the
cache creation. We can take that number and keep it, as we only ever
invalidate or replace.
Merge pull request #2634 from libgit2/cmn/tree-cache-count

tree-cache: correct the entry_count calculation
Remote paths: canonicalize UNC paths on Win32

Git for Windows will handle UNC paths only when in forward-slash
format, eg "//server/path".  When given a UNC path as a remote,
rewrite standard format ("\\server\path") into this ridiculous
format.
Merge pull request #2619 from ethomson/remotes_with_unc

Remote paths: canonicalize UNC paths on Win32
Merge pull request #2617 from linquize/describe-example

describe: add example