added some notes, cache dts in Date constructor
added some notes, cache dts in Date constructor

toobaz/pandas,louispotok/pandas,pandas-dev/pandas,amolkahat/pandas,amolkahat/pandas,nmartensen/pandas,cbertinato/pandas,linebp/pandas,louispotok/pandas,jmmease/pandas,linebp/pandas,toobaz/pandas,dsm054/pandas,winklerand/pandas,amolkahat/pandas,pratapvardhan/pandas,nmartensen/pandas,dsm054/pandas,Winand/pandas,GuessWhoSamFoo/pandas,Winand/pandas,kdebrab/pandas,jreback/pandas,pandas-dev/pandas,Winand/pandas,datapythonista/pandas,zfrenchee/pandas,Winand/pandas,cython-testbed/pandas,jorisvandenbossche/pandas,jmmease/pandas,Winand/pandas,winklerand/pandas,jreback/pandas,toobaz/pandas,cbertinato/pandas,jmmease/pandas,nmartensen/pandas,gfyoung/pandas,rs2/pandas,cbertinato/pandas,zfrenchee/pandas,MJuddBooth/pandas,kdebrab/pandas,GuessWhoSamFoo/pandas,toobaz/pandas,pratapvardhan/pandas,nmartensen/pandas,pratapvardhan/pandas,harisbal/pandas,toobaz/pandas,datapythonista/pandas,zfrenchee/pandas,cython-testbed/pandas,DGrady/pandas,cython-testbed/pandas,pratapvardhan/pandas,louispotok/pandas,zfrenchee/pandas,MJuddBooth/pandas,jreback/pandas,cython-testbed/pandas,kdebrab/pandas,winklerand/pandas,pandas-dev/pandas,winklerand/pandas,zfrenchee/pandas,cython-testbed/pandas,louispotok/pandas,jmmease/pandas,gfyoung/pandas,TomAugspurger/pandas,rs2/pandas,jmmease/pandas,winklerand/pandas,rs2/pandas,kdebrab/pandas,harisbal/pandas,amolkahat/pandas,dsm054/pandas,dsm054/pandas,GuessWhoSamFoo/pandas,jreback/pandas,Winand/pandas,harisbal/pandas,jorisvandenbossche/pandas,harisbal/pandas,amolkahat/pandas,MJuddBooth/pandas,GuessWhoSamFoo/pandas,gfyoung/pandas,TomAugspurger/pandas,jreback/pandas,pandas-dev/pandas,DGrady/pandas,kdebrab/pandas,DGrady/pandas,harisbal/pandas,nmartensen/pandas,winklerand/pandas,TomAugspurger/pandas,jorisvandenbossche/pandas,DGrady/pandas,cbertinato/pandas,datapythonista/pandas,nmartensen/pandas,linebp/pandas,gfyoung/pandas,DGrady/pandas,MJuddBooth/pandas,linebp/pandas,datapythonista/pandas,jmmease/pandas,linebp/pandas,dsm054/pandas,gfyoung/pandas,jorisvandenbossche/pandas,linebp/pandas,louispotok/pandas,pratapvardhan/pandas,MJuddBooth/pandas,cbertinato/pandas,DGrady/pandas,TomAugspurger/pandas,GuessWhoSamFoo/pandas,rs2/pandas