Add LLDB website and documentation in reStructuredText for Sphinx
The current LLDB website is written in HTML which is hard to maintain.
We have quite a bit of HTML code checked in which can make it hard to
differentiate between documentation written by us and documentation
generated by a tool.
In line with the other LLVM projects, I propose generating the
documentation with Sphix. I think text/rst files provide a lower barrier
for new or casual contributors to fix or update.
This patch adds a copy of the LLDB website and documentation in
reStructuredText. It also adds a new ninja target docs-lldb-html when
-DLLVM_ENABLE_SPHINX:BOOL is enabled.
This is the first step in having the website and documentation being
generated from the repository, rather than having the output checked-in
under the www folder. During the hopefully short transition period,
please also update the reStructuredText files when modifying the
Differential revision: https://reviews.llvm.org/D55376