DOC: Added an example of pitfalls when using astype
DOC: Added an example of pitfalls when using astype

 - [x] closes #13260    - [ ] tests added / passed   - [ ] passes
``git diff upstream/master | flake8 --diff``   - [ ] whatsnew entry

Author: Amol <pfrcks@gmail.com>

Closes #13278 from pfrcks/bug13260 and squashes the following commits:

035a177 [Amol] DOC: Final touches
c30209d [Amol] DOC: Cleaning up
278e922 [Amol] DOC: Some cleaning up
e1877bf [Amol] DOC: Restructured the documentation
f394045 [Amol] DOC: Cleaned up the documentation
705e1a5 [Amol] DOC: Added an example of pitfalls when using astype

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