Adds SymEngine::symbols() and allows Symbol.new to take a Ruby symbol

[translunar]

Fixes #33 and adds a convenience function, SymEngine::symbols which allows us to create multiple symbols simultaneously.

[certik]

I see that you test the following:

    #    x, y = SymEngine.symbols(%i{x y})
    #    x, y = SymEngine.symbols(%w{x y})
    #    x, y = SymEngine.symbols('x', 'y')
    #    x, y = SymEngine.symbols('x y')

Based on your comment above, should we also test these:

    #    x, y = SymEngine.symbols([:x, :y])
    #    x, y = SymEngine.symbols(['x', 'y'])

I can see that you test SymEngine::Symbol.new('x') and SymEngine::Symbol.new(:x) below.

[translunar]

%i{x y} is the same as [:x, :y], and %w{x y} is the same as ['x', 'y'].

I suppose we could also be exhaustive and test SymEngine.symbols(:x, :y), but it follows the same execution path as SymEngine.symbols('x', 'y'), so I think it's redundant.

[certik]

Ah ok. Then all is good.

[certik]

@MohawkJohn thanks for the PR! I left a minor comment. Otherwise it looks good.

[certik]

There is an error in Ruby 1.9.3 (https://travis-ci.org/symengine/symengine.rb/jobs/121473492):

/home/travis/.rvm/gems/ruby-1.9.3-p551/gems/rspec-core-3.4.4/lib/rspec/core/configuration.rb:1361:in `load': /home/travis/gems/symengine-0.1.0/spec/symbol_spec.rb:33: unknown type of %string (SyntaxError)

        @test_symbols_method.call(2, %i{x y})

                                        ^

/home/travis/gems/symengine-0.1.0/spec/symbol_spec.rb:33: syntax error, unexpected $end, expecting ')'

        @test_symbols_method.call(2, %i{x y})

Is this syntax not supported in Ruby 1.9.3?

[abinashmeher999]

Thanks a lot @MohawkJohn! This makes the interface better.

[certik]

I checked that the first release of Ruby 1.9.3 was at the end of 2011. For example, the first release of Python 2.6 was in 2008, but we are dropping it in SymPy this year. Python 2.7 was first released in 2010, and we definitely still support it --- but Python 2.7 is special in that it is the last version of Python 2.x, so it will be around for a long, long time. @MohawkJohn, what is the situation in Ruby --- what is the earliest version that we should support?

[translunar]

Oh, bleh. I didn't realize %i was introduced in Ruby 2.0.

http://stackoverflow.com/questions/17355177/what-is-the-origin-of-i-notation

It's probably reasonable to support 1.9.3. We should definitely cut off before 1.9.1. I'd say just require 1.9.3 or higher for now.

I've fixed the commit and tested it with 1.9.3-p551 now.

[certik]

Thanks, that sounds reasonable. Let's support 1.9.3 and up. All tests pass, so I am merging this.