Clean up autotools-related files and rpm spec file.

Clean up autotools-related files and rpm spec file.

 * Rename configure.in to configure.ac.
 * Delete install target from Makefile.am.
 * Change sslproxy.spec.in to suit new autotools-files.
 * Add conf/logrotate.d for logrotate config and rename the config file because
   this filename should be the same as its package name according to rpmlint.
 * Change to install README into docdir.

 Note: To build this package, follow these steps.
  1 Install automake, autoconf, libtool and other software required by
    SSLProxy.
  2 Checkout from git repository.
    % git clone <repository>
  3 Generate configure script, Makefile.in and other files.
    % cd sslproxy
    % autoreconf -if
  4 Build
    % ./configure    [*]
    % make
  5 Install
    % make install

  [*] You should specify following options to install as previous releases.
    % ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var \
             --libdir='${prefix}/lib64'