When parsing the patch image from a string, we split the string
by newlines to get a line-based view of it. To split, we use
`memchr` on the buffer and limit the buffer length by the
original length provided by the caller. This works just fine for
the first line, but for every subsequent line we need to actually
subtract the amount of bytes that we have already read.

The above issue can be easily triggered by having a source buffer
with at least two lines, where the second line does _not_ end in
a newline. Given a string "foo\nb", we have an original length of
five bytes. After having extracted the first line, we will point
to 'b' and again try to `memchr(p, '\n', 5)`, resulting in an
out-of-bounds read of four bytes.

Fix the issue by correctly subtracting the amount of bytes
already read.

Right now it is only possible to create remotes from a repository. While
this is probably the most common use-case, there are commands which make
sense even without a repository, e.g. the equivalence of `git
ls-remote`. Add a new function `git_remote_create_detached`, which
simply accepts a URL.

Add me. :)

In email, Torsten Bögershausen agreed that we could use his code
from core Git in libgit2 under the modified license.  Also, since
his work is the basis for much of the precompose unicode support,
I have added him to the AUTHORS file as well.

Signed-off-by: Sven Strickroth <email@cs-ware.de>

Add Florian Forster to hall of fame

Permission recieved from Florian Forster on Jan 07 2013 to include
any changes of his from core Git into LibGit2.