asplit: split up the input lines

We can define splitter words where a newline will be written to
the output - other words are written as before, as well as the original
LFs. Long lines can be made more readable.

Parameters:
-s[ep] {char}: specify the word separator in the input
-w: write the splitter item, too (otherwise it will be replaced with the 
    newline)
-c: containment, if the word contains the splitter, it will break the line
  (splitters can be subwords, too)
Other parameters are used as splitter words (in or-relation: any of them
will force a newline).
Splitters can be regular expressions, too, they must be specified with the
-r {regexp} option.

Examples:
acat ... | asplit -sep "," "<br>"
  -> the "<br>" symbols will be used as in the original html, that is
     it always starts a new line

acat ... | asplit -sep ' ' -c ple
  -> any word containing the 'ple' characters ('apple', 'plethora') will
     force a newline

acat ... | asplit -sep ' ' -r '^[(].*[)]'
  -> break up the lines at words that start with '(' and end with ')'