Fix up all doxygen warnings.

doc/Pitfalls.dox

@@ -17,7 +17,7 @@ especially if you got wrong results in statements where the destination appears
 \section TopicPitfalls_alignment_issue Alignment Issues (runtime assertion)
 
 %Eigen does explicit vectorization, and while that is appreciated by many users, that also leads to some issues in special situations where data alignment is compromised.
-Indeed, since C++17,  C++ does not have quite good enough support for explicit data alignment.
+Indeed, prior to C++17,  C++ does not have quite good enough support for explicit data alignment.
 In that case your program hits an assertion failure (that is, a "controlled crash") with a message that tells you to consult this page:
 \code
 http://eigen.tuxfamily.org/dox/group__TopicUnalignedArrayAssert.html
@@ -40,7 +40,7 @@ for(...) { ... w = C * v;  ...}
 
 In this example, the type of C is not a \c MatrixXd but an abstract expression representing a matrix product and storing references to \c A and \c B.
 Therefore, the product of \c A*B will be carried out multiple times, once per iteration of the for loop.
-Moreover, if the coefficients of A or B change during the iteration, then C will evaluate to different values.
+Moreover, if the coefficients of `A` or `B` change during the iteration, then `C` will evaluate to different values.
 
 Here is another example leading to a segfault:
 \code
@@ -72,7 +72,7 @@ Note that DenseBase::eval() is smart enough to avoid copies when the underlying
 \section TopicPitfalls_header_issues Header Issues (failure to compile)
 
 With all libraries, one must check the documentation for which header to include.
-The same is true with %Eigen, but slightly worse: with %Eigen, a method in a class may require an additional <code>#include</code> over what the class itself requires!
+The same is true with %Eigen, but slightly worse: with %Eigen, a method in a class may require an additional \c \#include over what the class itself requires!
 For example, if you want to use the \c cross() method on a vector (it computes a cross-product) then you need to:
 \code
 #include<Eigen/Geometry>