build tag file indexes of source code definitions

 ctags parses source code and produces a sort of index mapping
 the names of significant entities (e.g. functions, classes,
 variables) to the location where that entity is defined. This
 index is used by editors like vi and emacsen to allow moving to
 the definition of a user-specified entity.
 .
 Exuberant Ctags supports all possible C language constructions
 and multiple other languages such as assembler, AWK, ASP, BETA,
 Bourne/Korn/Z shell, C++, COBOL, Eiffel, Fortran, Java, Lisp,
 Lua, Makefile, Pascal, Perl, PHP, Python, REXX, Ruby, S-Lang,
 Scheme, Tcl, Verilog, Vim and YACC.