Cleanup core extensions

[weppos]

From #25

There's an small exception to my feedback. We can think about adding more .from_type methods with the purpose to simplify the core extensions provided in the core_extensions.rb file. In this case, we can create

# for the purpose of this example I separate Numeric
# into smaller classes
Money.from_fixnum(value, ...)
Money.from_float(value, ...)
Money.from_bigdecimal(value, ...)

class Fixnum
  def to_money(...)
    Money.from_fixnum(self, ...)
  end
end

class Float
  def to_money(...)
    Money.from_float(self, ...)
  end
end

class BigDecimal
  def to_money(...)
    Money.from_bigdecimal(self, ...)
  end
end

String deserves a special mention here because a String is a very data-rich money format. In fact, there are two types of string representations:

# with currency
"10 $"
"10 USD"
# without currency
"10"

This is the reason why we can try to provide two methods:

# A type-focused method, as for BigDecimal, Fixnum...
# which accepts only digit representations
# "1.0", "1000" and handle them as cents
Money.from_string

# A concept-focused method which implements a more advanced
# (and slow) detection mechanism
Money.parse(...)

The idea behind this change is to clean up the core_extensions by moving all the logic into the Money class.

[semmons99]

I like the idea of separate methods for handling simple strings versus complex ones. We'll probably need to think about a way of deprecating the old String#to_money so that it works more inline with Money#from_string and a new method to String that is a synonym for Money#parse.

[weppos]

My idea, was to implement a simple guessing mechanism.
If the string contains something different than digits, use #parse. Otherwise, use #from_string.

[semmons99]

so, something like a regex that detects anything other than digits, commas and periods?

[weppos]

Exactly.

[weppos]

I'm working on this.

[weppos]

Done. All tests passes.

I also took the time to cleanup the tests according to #28, increase documentation and test coverage.

http://github.com/RubyMoney/money/compare/issue_32

I didn't include the fix for #30 because I prefer to work on one ticket at time.

[weppos]

Cleanup core extensions (closed by 15460e9)