Make base64::config fields public again

These got swept up in the great privatizing of 2013.
Remove fk_anon
rewrite of shootout-fasta.rs

improvements:
 - no managed box
 - no virtual calls
 - no useless copy
 - optimizations (bisect is slower, limit tests, BufferedWriter...)
 - pass shootout test
 - should be as fast as the best official test

Thanks to @cmr and @eddyb for their help!
auto merge of #10931 : sfackler/rust/base64-visibility, r=alexcrichton

These got swept up in the great privatizing of 2013.
auto merge of #10935 : sanxiyn/rust/fk-anon, r=pcwalton
auto merge of #10933 : TeXitoi/rust/shootout-fasta-rewrite, r=alexcrichton

improvements:
 - no managed box
 - no virtual calls
 - no useless copy
 - optimizations (bisect is slower, limit tests, BufferedWriter...)
 - pass shootout test
 - 10 times faster
debuginfo: Always set column information to zero for source locations.
debuginfo: Clear debug source locations at beginning of functions.
debuginfo: Clear source positions where they'd confuse LLVM otherwise.
debuginfo: Create separate lexical block for function bodies.
debuginfo: Get rid of redundant argument copying with debuginfo activated
debuginfo: Use same behavior as Clang for calculating scope_line parameter when creating function DIEs.
debuginfo: Set the is_local_to_unit attribute of functions correctly
debuginfo: Set correct source position for function calls.
debuginfo: Add test cases for function prologue handling.
debuginfo: Added some documentation of source location management.