Hana v1.2.0, synced with Boost 1.65.0

This release contains

- Added support for set-theoretic operations on hana::map (see PR boostorg#350)
- Added the index_if function; like find_if but returns an optional index instead of an optional value
- various bug fixes

Merge 'develop' into 'master' for Hana version 1.2.0

Merge 'develop' into 'master' for Hana version 1.2.0

[bugfix] Fix incorrect result for `first` and `second` in nested pair…

… cases

[Travis] Fix installation of pcre

Hana v1.1.0, synced with Boost 1.64.0

Various bug fixes. The main improvement is better support for empty base
optimization in `hana::pair`, which should make it easier for the compiler
to optimize Hana away, at the cost of worst compile-times.

Merging develop into master for Hana version 1.1.0

Version 1.0.2 released with Boost 1.63.0

[string] Add a model of the Monoid concept

Fixes boostorg#117

Version 1.0.1 released in Boost 1.62.0