Add support for module private procedure symbols

[mcnulty]

• Add ProcedureSymbol struct used to hold data for symbol records with kinds: S_GPROC32, S_GPROC32_ST, S_LPROC32, S_LPROC32_ST, S_GPROC32_ID, S_LPROC32_ID, S_LPROC32_DPC, S_LPROC32_DPC_ID. These kinds are used for module private procedures.
• Add Procedure variant to SymbolData enum
• Add ProcedureFlags struct used to hold data from a CV_PROCFLAGS bit field. This is used by ProcedureSymbol
• Add support to pdb_symbols example to print names of module private procedures
• Add unit tests for parsing a few of the new symbol kinds, S_LPROC32 and S_GPROC32

[willglynn]

Merged. Thanks!