Split up the large tmath.cpp file

[lnsp]

Splitting up the large tmath.cpp file into logical units (like the tests) helps to maintain the project.

The logical units are

• abs.cpp
• cosecant.cpp
• cosine.cpp
• cotangent.cpp
• degrad.cpp
• equality.cpp
• explog.cpp
• factorial.cpp
• fcm.cpp
• power.cpp
• roots.cpp
• secant.cpp
• sine.cpp
• tangent.cpp
• vector.cpp

[lnsp]

Addressed in #27