Fix invalid XHTML in docs

[jwakely]

No description provided.

[codecov]

Codecov Report

Merging #99 into develop will increase coverage by 27.76%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           develop      #99       +/-   ##
============================================
+ Coverage    67.57%   95.33%   +27.76%     
============================================
  Files           33       22       -11     
  Lines         1437     1223      -214     
  Branches       534        0      -534     
============================================
+ Hits           971     1166      +195     
+ Misses          69       57       -12     
+ Partials       397        0      -397     

Impacted Files	Coverage Δ
...lude/boost/numeric/ublas/tensor/static_extents.hpp	100.00% <ø> (ø)
.../boost/numeric/ublas/tensor/fixed_rank_extents.hpp	94.28% <100.00%> (+17.14%)	⬆️
include/boost/numeric/ublas/vector_expression.hpp
include/boost/numeric/ublas/detail/definitions.hpp
include/boost/numeric/ublas/matrix_expression.hpp
include/boost/numeric/ublas/functional.hpp
include/boost/numeric/ublas/vector.hpp
include/boost/numeric/ublas/exception.hpp
...clude/boost/numeric/ublas/detail/vector_assign.hpp
include/boost/numeric/ublas/traits.hpp
... and 21 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a31e5cf...8cf9b57. Read the comment docs.

[jwakely]

The CI checks and coverage report appear to be meaningless, because there's no baseline for them. That means my pull request is treated as though it adds the entire library!

[shikharvashistha]

Hi @jwakely we've updated our documentation recently it would be available on boost.org in the next official release. The layout would look something like this. We've tried fix and improve upon almost all the issues which all of us were facing (including the XHTML's).

Best
@shikharvashistha