Fix broken links.
Typo fix
Merge pull request #19 from rui314/doc

Fix broken links.
Added ChangeLog entry for url-safe feature
Experimentally added sinpi etc.
Added tests for sinpi etc.
Removed unnecessary code
Fixed bug related to ghost continuation
Typo fix
Allow evaluating .gaucherc consistently in r7 mode
Defined some feature identifiers specified in R7RS appendix B
Added srfi-106
Install srfi-106.scm
Updated the list of builtin modules
Added dummy srfi-*.scm for srfis provided in different gauche modules

For example, srfi-18 is provided by gauche.threads, but a portable
program may want say (import (srfi 18)) and we need to make them happy.
Autogenerate srfi/N.scm to make (import (srfi N)) work
Adapted gen-staticinit to deal with glob patterns in SCMFILES list
Added r7rs 'environment'
Made 'use' and 'cond-expand' hygienic so that it can work in r7rs env
Fix library-has-module? to recognize R7RS define-library form