Create TODO.md for spanish-translation

[icculp]

[shannona]

My initial intent was to just translate based off 2.0, since 2.0.1 was still raw, but I didn't tell anyone that, oops.

My current goal is to create a 2.02 milestone as soon as the translations are done, with the theory that has all the bugs fixed and other corrections that turned up during the translations. I'm hoping that will allow easy access to any of those updates, as desired.

[csralvall]

Some things that we can take account in this TODO may be:

• [ ] Unify translation: wallet: monedero or billetera
• [ ] Unify translation: locktime: bloqueo de tiempo or tiempo de bloqueo (Domain specific)
• [ ] Unify translation: raw transaction: transacciones crudas or transacciones sin procesar (Domain specific)
• [ ] Unify translation: timestamp: marca de tiempo or estampa de tiempo (Domain specific)
• [ ] Unify translation: opcode: opcode or codigo de operacion (Domain specific)
• [ ] Unify translation: script: script or programa (Domain specific)
• [ ] Unify translation: caveat reader: Lectura de advertencia or Precaucion Lector
• [ ] Unify translation: Objectives for This Chapter: Objetivos para este capitulo or Objetivos de este capitulo
• [ ] Unify translation: translate 'variable names' inside <> in commands.
• [ ] Change connectors in main titles to lower case.

Opinion:

• Common anglicisms of domain specific words should be preferred over translations.
• Variable names inside <> in commands improve the reading if they are translated.

Also, after deciding about the unique translation of some words we could add them to the file mentioned in #466.