vbv: fix race condition in processRowEncoder, store row qp directly in m_pic->m_rowDiagQp.
add experimental support for interlaced content (field encoding) (refs #15)

* adds param.interlaceMode
* removes VUI params that are now handled automatically
* adds --no-interlace --interlace=tff|bff|prog|false CLI options
* signals interlace source flag, clears progressive source flag

This initial implementation requires the user to provide fields (half-height) in
the correct temporal order; so not very useful for exisitng Y4M or YUV
interlaced input files.

When interlacing is enabled, the encoder emits PictureTiming SEI messages that
indicate top or bottom field for the decoder.

--HG--
extra : amend_source : 4517604e38a59d6c7a9126b17b2cb450ac539fb4
pkgconfig: allow user-supplied lib folder (closes #40)
TEncSearch: validate unidirectional MVPs prior to trying MV0 bidir (closes #34)

This should fix some rare non-determinism as well as prevent the crash seen
in issue #34. [CHANGES OUTPUTS]