build: i18n: improve Intl build, add "--with-intl"

The two main goals of this change are:
 - to make it easier to build the Intl option using ICU
   (particularly, using a newer ICU than v8/Chromium's version)
 - to enable a much smaller ICU build with only English support
   The goal here is to get node.js binaries built this way by
   default so that the Intl API can be used. Additional data
   can be added at execution time (see Readme and wiki)

More details are in the PR https://github.com/joyent/node/pull/7719

In particular, this change adds the --with-intl= configure option to
 provide more ways of building "Intl":
 - full-icu picks up an ICU from deps/icu
 - small-icu is similar, but builds only English
 - system-icu uses pkg-config to find an installed ICU
 - none does nothing (no Intl)

For Windows builds, the "full-icu" or "small-icu" options are added to
vcbuild.bat.

Note that the existing "--with-icu-path" option is not removed from
configure, but may not be used alongside the new option.

Wiki changes have already been made on
 https://github.com/joyent/node/wiki/Installation
and a new page created at
 https://github.com/joyent/node/wiki/Intl
(marked as provisional until this change lands.)

Now, a summary of the changes:

* README.md : doc updates

* .gitignore : added "deps/icu" as this is the location where ICU is
  unpacked to.

* Makefile : added the tools/icu/* files to cpplint, but excluded a
  problematic file.

* configure : added the --with-intl option mentioned above.
  Calculate at config time the list of ICU source files to use and data
  packaging options.

* node.gyp : add the new files src/node_i18n.cc/.h as well as ICU
  linkage.

* src/node.cc : add call into
  node::i18n::InitializeICUDirectory(icu_data_dir) as well as new
  --icu-data-dir option and NODE_ICU_DATA env variable to configure ICU
  data loading. This loading is only relevant in the "small"
  configuration.

* src/node_i18n.cc: new source file for the above Initialize.. function,
  to setup ICU as needed.

* tools/icu : new directory with some tools needed for this build.

* tools/icu/icu-generic.gyp : new .gyp file that builds ICU in some new
  ways, both on unix/mac and windows.

* tools/icu/icu-system.gyp : new .gyp file to build node against a
  pkg-config detected ICU.

* tools/icu/icu_small.json : new config file for the "English-only" small
  build.

* tools/icu/icutrim.py : new tool for trimming down ICU data. Reads the
  above .json file.

* tools/icu/iculslocs.cc : new tool for repairing ICU data manifests
  after trim operation.

* tools/icu/no-op.cc : dummy file to force .gyp into using a C++ linker.

* vcbuild.bat : added small-icu and full-icu options, to call into
  configure.

build: i18n: try to fix toolset dependencies again