cat: Add options -s.

* src/dctc/java/com/dataiku/dctc/command/Cat.java: Squeeze blank line
  if duplicate.
cat: Add an empty line before the header.

* src/dctc/java/com/dataiku/dctc/command/Head.java: Here.
cat: Ask if we need to continue to read the stream.

* src/dctc/java/com/dataiku/dctc/command/cat/CatStop.java: The
  interface.
* src/dctc/java/com/dataiku/dctc/command/cat/ContinueCatStop.java:
  Always continue.
* src/dctc/java/com/dataiku/dctc/command/cat/CatAlgorithmFactory.java:
  Set a default behavior for cat.
* src/dctc/java/com/dataiku/dctc/command/cat/LinumCatAlgorithm.java:
  Ask if continue or not to read the stream.
head: Implementation of CatStop for Head.

* src/dctc/java/com/dataiku/dctc/command/cat/HeadCatStop.java: Told
  false after =n= was read.
head: Factory for the head algorithm.

* src/dctc/java/com/dataiku/dctc/command/cat/CatAlgorithmFactory.java:
  Here.
file: Make standard file public.

* src/dctc/java/com/dataiku/dctc/file/StandardFile.java: Here.
head: Use the new implementations.

* src/dctc/java/com/dataiku/dctc/command/Head.java: Here.
wtf: Java don't know how to parse int.

* src/core/java/com/dataiku/dip/utils/IntegerUtils.java: Need to drop
  all signs.
wtf: Apache don't what is a numeric.

* src/dctc/java/com/dataiku/dctc/command/Head.java: A numeric coulds
  has signs.
head: Use a right integer parser.

* src/dctc/java/com/dataiku/dctc/command/Head.java: Here.
cat: Extend cat printer interface.

* src/dctc/java/com/dataiku/dctc/command/cat/CatPrinter.java: Here.
* src/dctc/java/com/dataiku/dctc/command/cat/AbstractCatPrinter.java:
  Default implementation here.
* src/dctc/java/com/dataiku/dctc/command/cat/CatAlgorithmFactory.java:
  Adjust.
* src/dctc/java/com/dataiku/dctc/command/cat/LinumCatAlgorithm.java:
  Don't print header and end of line for each line.
* src/dctc/java/com/dataiku/dctc/command/cat/SimpleCatPrinter.java:
  Print the header and the end of line when printing the line.
cat: new printer for head.

* src/dctc/java/com/dataiku/dctc/command/cat/HeadCatPrinter.java:
  Print only the head but the =n= last line.
head: Implements -n -K.

* src/dctc/java/com/dataiku/dctc/command/cat/CatAlgorithmFactory.java:
  Implements the options `-n' when K is negative.
int-utils: Really authorize _. Add comma to the list.

* src/core/java/com/dataiku/dip/utils/IntegerUtils.java: Authorize to
  write 1_024 or 1,024.
int-utils: Add comment on unit parsing.

* src/core/java/com/dataiku/dip/utils/IntegerUtils.java: Could not add
  unit parsing. With hexadecimal number the tools has more power.