(maint) Remove openssl version from README.

Removing the openssl version requirement from the README.  We have no
hard requirement on openssl version; the version presented here was
mostly a suggestion.  Removing it to avoid confusion.
Merge pull request #232 from peterhuene/maint

(maint) Remove openssl version from README.
(CFACT-165) Build cfacter for lucid and squeeze
(maint) Define a minimum of 1 job to run

Prior to this commit, on some systems, `nproc` wasn't available on the
system. Since we use this to define the job threading for building with
cmake, having nproc not be defined left us calling `make -j`. This
basically tells make to build with an unlimited number of jobs, eating
up all available system memory, making the build fail with `virtual
memory exhausted: Cannot allocate memory`. This commit changes how we
are defining the number of jobs to thread at once. We want to use
`nproc` when we can, but when we cannot, we just set it at `1`. Ideally
we build with `nproc+1`, so this ensures that we are not eating up all
available memory, and are running jobs at maximum efficiency when
possible.
(maint) Update buildtime requirements

CFacter has a soft requirement on openssl >= 1.0.1g, but it will still
build with other versions of openssl. Since we want to enable as much
functionality in our builds, we want to link against openssl if
possible. Older versions of debian/ubuntu only have openssl in the 0.9.8
range, so when it comes to runtime dependencies, we want to allow the
user to install whatever libssl is available on the system. In this
case, we have a choice between libssl1.0.0 (for openssl1.0.1) or
libssl0.9.8.

Also, it was a little silly that we were using libcurl4-gnutils, rather
than libcurl4-openssl. I believe the original choice was rather
arbitrary, but since we're using openssl here anyway, it makes sence to
use that version of libcurl.