Improvement of error messages for pattern macros

[Kodiologist]

Advancements to funcpaserlib such as vlasovskikh/funcparserlib#52 should allow improving error messages produced while parsing calls to Hy's core pattern macros. In an error like the below example, expected: some(...) could probably be changed to expected symbol.

Traceback (most recent call last):
  File "<string>", line 1
    (defmacro 1)
              ^
hy.errors.HySyntaxError: parse error for pattern macro 'defmacro': got unexpected token: hy.models.Integer(1), expected: some(...)

It's conceivable that most of the patterns for Hy's core macros are too complex to admit useful automatic descriptions of the kind of form that's expected. If so, it's probably better to forget about this than to hand-write descriptions for lots of patterns. Manually writing lots of error messages like that is the sort of thing I intended to avoid by using funcparserlib in the first place.

A simpler sort of improvement would be rewording "unexpected end of input", as provoked by e.g. (defmacro), to something that makes it clearer that the form, as opposed to the entire file, ended prematurely.