Update to version 20.

----------------
Release 20
----------------
    * Fixes: model names starting with a number (1n4001) are now correctly parsed. The .global
      command has been reinstated (it was previously disabled) and error messages now display
      the corresponding line numberin the input deck.
    * New Features: .measure command for transient, ac and dc analyses (still not complete, e.g.
      DERIV is missing).
    * Devices: Updated BISM4 model to revision 4.6.5. Added PWL (PieceWise Linear) functionality
      for B (arbitrary generator) sources.

----------------
Release 19
----------------
Reveals an important work in compile scripts, many bug fixes in memory management, interface, and
work in device models.

    * Compile scripts: tclspice and ADMS compiling fixes. Architecture compiling fixes for SunOS,
      MS Visual Studio, MINGW, Cygwin.
    * Memory management: fixed memory leaks, modifies memory management for MS Windos, integration of
      espice bugfixes and enhancements, bug fixes in plots and cli interface.
    * Rework of BSim models, integration of EPFL-EKV model V2.63, ADMS models mextram, hicum0, hicum2.

----------------
Release 18
----------------
Rework-18 is introduces several new features into ngspice. This is a major
release that comes after more than three years. During the silent years
ngspice developers worked in CVS to stabilize and introduce new features
into the simulator.

- Tclspice simulator library has been merged with ngspice. Now you can
  compile ngapice or tclspice by asserting a configure switch. See README.tcl
- New options have been introduced: brief, listing, autostop and scale
- Support for .lib file has been introduced. This allows the use of
  third party model libraries in ngspice.
- .measure statements: avg, integ, rms, max, min, delay, param
- .global statements t support for global nodes whose name is not expanded
  when flattening the netlist.
- .func macros for inlining functions into netlists.
- Improved the numparam library to support fully parametrized netlists.
- BSIM model binning.
- new multi-input gate VCVS using XSPICE extensions.


(dmcmahill)