[gtksourceview: 2/2] lean.lang: add LEAN language specification

[Christian Hergert <chergert src gnome org>]

commit e990defcb67fc320d0b08eb225bc543f8ff4ee9e
Merge: 8dbde2a7 46c6c210
Author: Christian Hergert <christian hergert me>
Date:   Fri Sep 17 20:48:11 2021 +0000

    lean.lang: add LEAN language specification
    
    add syntax highlighting for Lean
    
    https://leanprover.github.io/about/
    
    See merge request GNOME/gtksourceview!208

 data/language-specs/lean.lang       | 163 ++++++++++++++++++++++++++++++++++++
 tests/syntax-highlighting/file.lean |  15 ++++
 2 files changed, 178 insertions(+)
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