Implicits Chapter: Edits to docstrings, plus one code change

[jonboiser]

1. Fix markdown list at line 11
2. Add code backticks to some terms
3. Some edits (colons and capitalizing Implicit Function Parameters) for consistency w/ rest of doc
4. On line 105

-def asDefaultImplicits(res0: Float) {
+def asDefaultImplicits(res0: BigDecimal) {

Since, I had to manually cast the answer on the koan to Float. IDK if this requires a change on somewhere else in the code, but can do it if you point me to the file.

[ghost]

Great improvements, thanks a lot! The test code for the modified exercise can be found here.

[jonboiser]

@dialelo I think the fix was pretty simple. Even removed a line of what looked like dead code. Could you review?

[raulraja]

@jonboiser Looks great. Thanks for your contribution!