added option ADDED_LIB_TARGET_NAME_OUT to TRIBITS_ADD_LIBRARY

If TRIBITS_ADD_LIBRARY() is called with this keyword and a respective value,
the value is set to the library name that was added, and set to nothing if no
library was added.

Fixes part of bug #4.
Return added target/test names from TRIBITS_ADD_XXX() wrapper functions

Largely fixes bug #4.

Still missing: TRIBITS_ADD_ADVANCED_TEST() and tests.
be a little more economic with vertical space
remove trailing whitespace in all *.cmake files

This helps keeping future commits clean in this respect.
Was never used.
Shortenling names of packages and dirs to MixedLang and WithSubpackages (dir move)

This is the first step, moving the directories.  Git likes it when you move
files first, then change them.

I also wanted to use lower case names for the subpackage dir names.
Shortenling names to MixedLang and WithSubpackages

This makes the substitutions:

  MixedLanguage => MixedLang
  PackageWithSubpackages => WithSubpackages
  SubpackageA => A
  SubpackageB => B
  SubpackageC => C

I also I changed the directory names:

  mixed_language => mixed_lang
  package_with_subpackages => with_subpackages
  package_with_subpackages/A => with_subpackages/a
  package_with_subpackages/B => with_subpackages/b
  package_with_subpackages/C => with_subpackages/c

The names of the subpackages are now shorter and easier to type and read.  The
directory names are shorter and are now all lower-case as is convention
adopted from Trilinos.

All of the tests have been updated too.
Merge remote-tracking branch 'nico-github/return_lib_name'
Fixed a few minor typos.
Added documentation and a test for ADDED_LIB_TARGET_NAME_OUT (TriBITS #4, #29)

Fixes #4.

1/4 of the way to addressing #29.
Updated generated files.