Added single_peak_search code in eris/algorithms

This uses a golden ratio section search to efficiently search a domain
for a function max.  Obviously it only works when the function is
single-peaked and has no perfectly-flat sections.

This also includes a test script.
Documentation fix (exception class changed names)
Fixed test script for new Positional<A> wrapper
Fixed DEBUG -> ERIS_DBG macro
Don't need 'extern' for function export