Introducing locator functionality to AST

[nikololiahim]

Initially, this pull request was intended to introduce identifiers with locators (^.^.^.apple, $.self). However several other things have to be done before this:

1. In order to test and debug the implementation, we need a working pretty-printer.
2. Existing pretty-printer had some issues that needed to be fixed.
3. In order to correctly pretty print some AST arrangements, parser needs to recognize single-line abstractions.

What was done:

1. Explicit locator chains are parsed into EOSimpleAppWithLocator. For example, EO code ^.^.^.a gets parsed into:

EOSimpleAppWithLocator("a", 3)

Previously, such expressions were parsed as:

EODot(EODot(EODot(EOSimpleApp("^"), "^"), "^"), "a")

2. We created an algorithm for replacing plain EOSimpleApps with EOSimpleAppWithLocators. The following code without locators:

[] > obj
  [self] > method
    self > @
  [method] > shadowedMethod
    method > @
  [] > notShadowedMethod
    method > @

[] > notShadowedObj
  obj > @
  
[] > shadowedObj
  [obj] > method
    [] > innerMethod
      obj > @
    obj > @

[] > outer
  [] > self
    256 > magic
    [] > dummy
      [outer] > dummyMethod
        outer > @
      outer.self > @
    self "yahoo" > @
  [self] > method
    self.magic > @

gets turned into the following code with locators:

[] > obj
  [self] > method
    $.self > @
  [method] > shadowedMethod
    $.method > @
  [] > notShadowedMethod
    ^.method > @
[] > notShadowedObj
  ^.obj > @
[] > shadowedObj
  [obj] > method
    [] > innerMethod
      ^.obj > @
    $.obj > @
[] > outer
  [] > self
    256 > magic
    [] > dummy
      [outer] > dummyMethod
        $.outer > @
      ^.^.^.outer.self > @
    ^.self > @
      "yahoo"
  [self] > method
    $.self.magic > @

3. Existing tests were adapted and extended. The most prominent one is that the property:

ast->toEO == ast->toEO->parsed->toEO

now holds for both the parsed and pretty-printer.

[nikololiahim]

@fizruk I have updated this PR's message.