Update .travis.yml

comment-out "apt-get install graphviz", it takes too much time because it depends on LaTeX. Maybe it's better to move this operation on OS X side where homebrew can build graphviz without LaTeX.

[skip ci]
Update src/CMakeLists.txt to increase stack size for windows build

[skip ci]
Fix typo

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix bug in display_decimal. Add more mpq tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix spaces

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix example

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Track recursion depth at normalizer. Add fluid let template.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add option to control maximum recursion depth in the expression normalizer

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

Conflicts:
	src/tests/kernel/normalize.cpp
Add head_beta function

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add head_beta tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Refactor expression equality

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Refactor expression equality