Ability to get related articles and specify page number

[runtarm]

This PR introduces two new command line options, --related and --page.

Ability to get related articles of an article with --related or -r
To use --related=ARTICLE_ID, first get the article ID from a normal search result.

$ scholar.py -c 1 --author "albert einstein"
         Title Can quantum-mechanical description of physical reality be considered complete?
           URL http://journals.aps.org/pr/abstract/10.1103/PhysRev.47.777
          Year 1935
     Citations 14224
      Versions 134
    Cluster ID 8174092782678430881
    Article ID odSh4BM2cHEJ
      PDF link http://link.aps.org/pdf/10.1103/PhysRev.47.777
Citations list http://scholar.google.com/scholar?cites=8174092782678430881&as_sdt=2005&sciodt=0,5&hl=en
 Versions list http://scholar.google.com/scholar?cluster=8174092782678430881&hl=en&as_sdt=0,5
       Excerpt Abstract In a complete theory there is an element corresponding to each element of reality. A sufficient condition for the reality of a physical quantity is the possibility of predicting it with certainty, without disturbing the system. In quantum mechanics in the case of two physical  ...

Notice the new Article ID field under Cluster ID, then use it like this:

$ scholar.py -c 3 --related odSh4BM2cHEJ
     Title Can quantum-mechanical description of physical reality be considered complete?
           URL http://journals.aps.org/pr/abstract/10.1103/PhysRev.47.777
          Year 1935
     Citations 14224
      Versions 134
    Cluster ID 8174092782678430881
    Article ID odSh4BM2cHEJ
      PDF link http://link.aps.org/pdf/10.1103/PhysRev.47.777
Citations list http://scholar.google.com/scholar?cites=8174092782678430881&as_sdt=2005&sciodt=0,5&hl=en
 Versions list http://scholar.google.com/scholar?cluster=8174092782678430881&hl=en&as_sdt=0,5
       Excerpt Abstract In a complete theory there is an element corresponding to each element of reality. A sufficient condition for the reality of a physical quantity is the possibility of predicting it with certainty, without disturbing the system. In quantum mechanics in the case of two physical  ...

         Title On the einstein podolsky rosen paradox
           URL http://books.google.com/books?hl=en&lr=&id=pufUCgAAQBAJ&oi=fnd&pg=PA7&dq=related:odSh4BM2cHEJ:scholar.google.com&ots=APbyikjWM5&sig=aAmubRTjB4OdX1sieBV9iTwdBAI
          Year 1964
     Citations 10091
      Versions 31
    Cluster ID 5285903270378747828
    Article ID tDcAvARNW0kJ
      PDF link http://cds.cern.ch/record/111654/files/vol1p195-200_001.pdf
Citations list http://scholar.google.com/scholar?cites=5285903270378747828&as_sdt=2005&sciodt=0,5&hl=en
 Versions list http://scholar.google.com/scholar?cluster=5285903270378747828&hl=en&as_sdt=0,5
       Excerpt THE paradox of Einstein, Podolsky and Rosen [1] was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional vari-ables were to restore to the theory causality  ...

         Title Experimental test of Bell's inequalities using time-varying analyzers
           URL http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.49.1804
          Year 1982
     Citations 3996
      Versions 38
    Cluster ID 15622202840203047756
    Article ID TLNmk7Y2zdgJ
      PDF link http://link.aps.org/pdf/10.1103/PhysRevLett.49.1804
Citations list http://scholar.google.com/scholar?cites=15622202840203047756&as_sdt=2005&sciodt=0,5&hl=en
 Versions list http://scholar.google.com/scholar?cluster=15622202840203047756&hl=en&as_sdt=0,5
       Excerpt Abstract Correlations of linear polarizations of pairs of photons have been measured with time-varying analyzers. The analyzer in each leg of the apparatus is an acousto-optical switch followed by two linear polarizers. The switches operate at incommensurate  ...

Ability to specify the page number to retrieve more results with --page
To use --page=PAGE, just specify a page number. It can be used together with -c like this:

$ scholar.py -c 20 --page 3 --author "albert einstein"