Refactoring code

Now the object doesn't respond to '.attribute_name'.
Removed unecessary activesupport gem
Updated rspec version to use the new rspec syntax
Update typecaster to call class methods on typecaster's type classes
Add README
Bump up version
Fix typo on README
Add text parse
Return a hash instead of a array when parse a text
Created TypeCaster::Parser

this object is responsible to read an file and parses it according with the descriptor

also added .rvmrc to gitignore
README updated
Fix typo on README
Remove unecessary string concatenation on parser
Change option's name `:class` to `:caster` changing
API to:

attribute :foo, :size => 10, :caster => FooTypecaster
Add `with_options` method in order to improve the
gem API to avoid repetition in declarations of the
attribute method.

Now we can also define the attributes that way:

with_options :caster => FooTypecaster, :size => 2 do
  attribute :foo, :position => 2
  attribute :bar, :position => 1, :default => '*'
end

With this implementation also it's necessary to add 
a position for each attribute that defines the 
order of the data.
Fix bug that was overriding options of the attribute 
when called outside of the with_options block
Remove blank line in hash file
Update project's README

Add description about `with_options` method
And update the demonstration of the API
Fix indentation in project's README
Add a simple validation when defining some values inside the Typecaster object

Sometimes we make some typos when writing a new object
in greater objects is harder to find where it happens.
this validation checks with a friendly message instead the ugly

```
NoMethodError:
   undefined method `[]=' for nil:NilClass
```

now it will raise something like that

```
attribute xpto is not defined
```