Allow specifying location of PCRE

[bklang]

Many systems have PCRE installed in non-default locations. In my case, Macports installs pcre to /opt/local. It would be nice if we could tell ruby_speech where to find pcre.h. My suggestion is to use

--with-pcre=/opt/local

Where pcre.h is expected to be within the /opt/local/include directory, and libpcre is expected to be at /opt/local/lib.

[bklang]

To answer my own question, this seems to do it:

bundle config build.ruby_speech --with-opt-dir=/opt/local