Modified CHARMM crd format reader and writer:

  - fixed continuous residue numbering (BZDNG-286)
  - fixed bug with empty lines
  - fixed bug with reading residue name in std format
  - write b_factor in EXT format
  - segment name is now cname instead of 'MOL'
  - fixed alignment of residue name in std format
  - add documentation
  - add unit tests
  - possibility to request EXT format