added requirement files

requirements/common.txt

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+# Contains common requirements 
+Pygments>=2.3.1
+argparse==1.4.0
+cssselect==1.1.0
+lxml>=4.2.5
+pyquery==1.4.1
+requests==2.24.0
+cachelib==0.1
+appdirs==1.4.4
+keep==2.9

requirements/dev.txt

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+# Contains development specific requirements and imports common requirements
+-r common.txt

requirements/prod.txt

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+# Contains production specific requirements and imports common requirements
+-r common.txt