evtr: initial implementation of a DSL

evtr: initial implementation of a DSL

libevtr:
- abstract out the hash table, convert to using uintptr_t's
  internally
- move a bunch of fields and most of the error logic from
  evtr to evtr_query
- don't try to resolve format strings to id's and reject
  records that don't match early; this needs way more care
  now that we might want to interpret the format strings
- start implementation of a minimal Domain Specific Language
- add the ability to filter based on the event type
- lots of fixes all around

evtranalyze:
- catch up w/ API changes in libevtr
- add toy 'stats' command