DWARF4 introduced a new attribute for describing bitfields,
DW_AT_data_bit_offset. This attribute replaces use of the attribute
DW_AT_bit_offset in DWARF version > 4.

Added heuristic to determine when to use the DataBitOffset or BitOffset field
in order to support compile units using a DWARF version greater than or less
than 4.

Fixes #49

dwarf.go was added to prevent applying elf relocations prior to DWARF parsing.
However, dwarf.go is currently unnecessary due to improved support for ELF
relocations in the debug/elf library.

Fixes #45

Anonymous fields in structure types were previously named using the
byte offset of the field into a structure. However, this led to name
collisons when reading structures that have multiple unnamed fields at
the same offset. This name collision then led to the overwriting some
anonymous fields.

Modified anonymous field labeling from using the byte offset to using
the sum of the number of anonymous fields in current structure. This
avoids the observed name collisons.

Fixes #50
Fixes #23