Fixes prefix operators
Refines identifiers and symbols

* symbols can now be keywords again, e.g. 'this
* foo + foo_++(42) is now correctly parsed as
  Infix(foo, +, App(foo_++, 42))
* identifiers can start and end with underscores and can have
  underscores in between
* __ is recognized as valid identifier
Reverts accidental change in test/op_suffix_application.scala
Turns the tests from *.scala to *.spt

*.scala should really only contain valid scala code (which will be
accepted by the scala compiler), which was not true
for most of the test files before.

+ Spoofax tests can be automated and check against the resulting parse
tree. This is way more reliable than only manually checking if there are
no errors or ambiguities.
Adds tests for simple expressions and refines them

Got one ambiguity with full qualified name class instantiations and
applications, but the preference on the instantiations does
unfortunately not help.
Reduces fqn class instantiation != designator problem
Fixes ambiguity with fqn class instantiations
Fixes imports (were broken by last commit)
Removes ambiguity with literals and postfix expr
Readds wildcard types
Adds special syntax for one-argument result expressions
Adds test and description for template body problem
Allows free layout in certain expressions
Adds another test to template statement problem
Fixes literals

* hex numerals were not parsed correctly before
* did not have support for unicode characters '\uxxxx'
Changes pattern matching

* replaces CaseClauses with CaseClause+
* introduces new EOCBlockStatSemi with EOC symbol
  EOC is an empty production, which must be followed by the token 'c'.
  The sole purpose of this is to successfully parse multiple case
  patterns on the same line.
Adds operator precedence for infix expressions
Changes on floats

Floats ending with "." are deprecated in Scala 2.10, so there is no need
to support this syntax.
Some changes on identifiers

* infix operations starting with letters now also support the operator
  suffix (e.g. should_==)
* identifiers starting with keywords should no longer be confused with
  other productions (e.g. classOf is never the start of a class
  definition)
Changes on infix expressions

Infix expressions with letter operators can also have other infix
expressions as right hand side => disambiguation was wrong