Always prepend space to -DPROCESSOR_COUNT

This prevents issues when something is already declared in DEFS.

Originally submitted here:

  https://github.com/wincent/Command-T/pull/60

As noted in the comment there:

  "Just for the record, this caused issues on Fedora 20 i386 (the x86_64
  build is ok)"

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Merge remote-tracking branch 'voxik/add-defs-space'

* voxik/add-defs-space:
  Always prepend space to -DPROCESSOR_COUNT
Add installation note about Fedora

Since Command-T is packaged for Fedora, installing from system
repository should be the preferred way.

Originally submitted here:

  https://github.com/wincent/Command-T/pull/61

with minor amendments applied here (capitalization and an edit for
brevity).

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Merge remote-tracking branch 'voxik/patch-1'

* voxik/patch-1:
  Add installation note about Fedora
Make sanity check more sane

Having a processor count of 0 wouldn't be very sane either, so let's
clamp within the range of 1..32 (inclusive).

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Defer processor count detection until runtime

As suggested here:

  https://wincent.com/issues/2133

Copying the text of the linked issue:

  You assume, that the Ruby extension is build on the same machine,
  where the code is executed. This assumption is invalid for Fedora.
  When I package command-t for use with Fedora, the extension is built
  on Koji builder. There might be powerful CPUs with plenty of cores,
  but it says nothing about my machine.

I've moved the processor count detection into a runtime method on a new
CommandT::Util module (seeing as there isn't any other obvious place to
put it right now). The count is memoized to avoid exposure.

In the C code that consumes the count (the Matcher#sorted_matches_for
method), I do do a `nil` check because there are a few callers in places
like the test suite that shouldn't have to bother with passing it in,
but I don't worry about more robust sanity checking, leaving that up to
the CommandT::Util method instead.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Update docs for 1.6.1 release

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Remove "archive" Rake task

I'm not going to maintain the "releases" branch anymore, for reasons
described in the README on that branch, so this Rake task no longer has
a reason to exist.

Signed-off-by: Wincent Colaiuta <win@wincent.com>