Improve error message.
... for ChannelError and APIMisuseError
Before this commit, When rl returns error, we don't know
The actual parameter which caused the error.
By returning parameterised `String` instead of predefined `&'static str`,
We can give a caller improved error message.
TestLogger now has two additional methods
1. `assert_log_contains` which checks the logged messsage
has how many entry which includes the specified string as a substring.
2. `aasert_log_regex` mostly the same with `assert_log_contains`
but it is more flexible that caller specifies regex which has
to be satisfied instead of just a substring.
For regex, tests now includes `regex` as dev-dependency.
13 files changed: