ginac benchmark: print the time
Travis: Simplify .travis.yml

Do all the actual work in bin/test_travis.sh
No need to use semicolons anymore
Refactor Travis tests

Few changes:

    * Don't specify a variable if a default value is used
    * The various external library configuration tests are done in the first
      section.
    * Run most of the tests in out of tree builds, as those should be the
      default. Only run a few simple tests in the tree to make sure that things
      work.
    * The matrix section just tests a simple Release mode with various Python
      versions
Release is the default build, don't specify it
Only pass nonempty options to cmake
LambertW class Basic API
Added all the methods for `LambertW` class
Added tests for `LambertW` class
Merge pull request #200 from sushant-hiray/lambertw

Added the `LambertW` class. Merge #200
Merge pull request #199 from certik/travis

Travis: Simplify .travis.yml
Fix for issue #204

If Mul dictionary contains numbers we add a `*` in printing
Fix the issue using iterators

Problem arose when `coef_` and first item in the `dict_` were both numeric. Previously
`*` sign was not inserted between `coef` and the first entry in the `dict_`.
Add tests for printing

Also removed the check for `dict_.empty()` as it is checked as an assertion
insied constructor.
Add brackets around exponent when the exponent is not an `Integer` or a `Symbol`
Merge pull request #205 from thilinarmtb/Fix_#204_print_error

Fix for issue #204
Merge pull request #193 from certik/ginac

ginac benchmark: print the time
Merge branch 'master' into install
Travis: test "make install"

We try to compile and run the test_basic.cpp test just to see if it works.