Issue #196 : Pipelining duplication lambda_t and map_t

[ssoelvsten]

Closes #196 .

Proposed Changes

• Deprecates lambda in favour of map (with deprecation warnings)
• Deprecates exclude_lambda in favour of a new filter_map (with deprecation warnings). This is such that a more consistent naming scheme is provided.
  • Currently a std::pair<T,bool> is used. Is it of interest to also support a std::optional<T> introduced in C++17? Based on this StackOverflow a pair is in terms of performance faster if the element constructor is cheap.
• Fixes the documentation for exclude_lambda_t has the meaning of .first and .second the wrong way around compared to its implementation.

Possible Changes (but I cannot tell whether these are desired)

• pipelining/map.h also has alternatives to map, i.e. map_temp, map_sink and push_map. Should the same also be made for pipelining/filter.h and pipelining/filter_map.h?
• tpie/pipelining.h imports pipelining/map.h but not pipelining/filter.h. Is this on purpose?
• There are no unit tests for map, filter and filter_map and looking at test/pipelining.cpp and test/pipelining2.cpp I cannot exactly tell how I should add these.