Pytables selection enhancement & docs update for HDF5 tables
1. added **str** (to do **repr**)
2. row removal in tables is much faster if rows are consecutive
3. added Term class, refactored Selection (this is backwards compatible)
    Term is a concise way of specifying conditions for queries, e.g.
   
   ```
   Term(dict(field = 'index', op = '>', value = '20121114'))
   Term('index', '20121114')
   Term('index', '>', '20121114')
   Term('index', ['20121114','20121114'])
   Term('index', datetime(2012,11,14))
   Term('index>20121114')
   ```
   
    updated tests for same
   
     this should close GH #1996
4. added docs for HDF5 table in io.html
5. append on a table that didn't exist was failing (because of testing of the index_kind attribute first - which may not exist)
    fixed & added test
6. added create_table_index method to create indicies on tables (which, btw now works quite well as Int64 indicies are used as opposed to the Time64Col which has a bug); includes a check on the pytables version requirement
   
   this should close GH #698
7. added min_itemsize as a paremeter to append; allows bigger default indexer columns upon table creation (even if you don't append something that big - but might later, avoid the truncation issue)
8. incorporated 0.9.1 whatsnew docs for where & mask into Indexing Section of main docs
