Split bcc.table.BPFTable into multiple type-specific classes

BPFTable contained all of the logic for multiple table types, which is
incorrect since a bpf table has either hash or array behavior.
Additionally, some methods on the classes aren't valid for some table
types. Create HashTable, Array, ProgArray, and PerfEventArray classes to
contain this behavior.

In future, the new Array class and its children should behave more like
an array than a dict as it currently does.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

src/python/bcc/__init__.py

@@ -26,7 +26,7 @@ import sys
 basestring = (unicode if sys.version_info[0] < 3 else str)
 
 from .libbcc import lib, _CB_TYPE
-from .table import BPFTable
+from .table import Table
 
 open_kprobes = {}
 open_uprobes = {}
@@ -64,7 +64,9 @@ class BPF(object):
     _libsearch_cache = {}
     _lib_load_address_cache = {}
     _lib_symbol_cache = {}
-    Table = BPFTable
+
+    # defined for compatibility reasons, to be removed
+    Table = Table
 
     class Function(object):
         def __init__(self, bpf, name, fd):
@@ -234,7 +236,7 @@ class BPF(object):
             if not leaf_desc:
                 raise Exception("Failed to load BPF Table %s leaf desc" % name)
             leaftype = BPF._decode_table_type(json.loads(leaf_desc.decode()))
-        return BPF.Table(self, map_id, map_fd, keytype, leaftype)
+        return Table(self, map_id, map_fd, keytype, leaftype)
 
     def __getitem__(self, key):
         if key not in self.tables: