doc: fix a few small typos

PR #230

src/writer.rs

@@ -478,7 +478,7 @@ impl WriterBuilder {
  }
 }
 
-/// A already configured CSV writer.
+/// An already configured CSV writer.
 ///
 /// A CSV writer takes as input Rust values and writes those values in a valid
 /// CSV format as output.
@@ -518,7 +518,7 @@ struct WriterState {
  header: HeaderState,
  /// Whether inconsistent record lengths are allowed.
  flexible: bool,
- /// The number of fields writtein in the first record. This is compared
+ /// The number of fields written in the first record. This is compared
  /// with `fields_written` on all subsequent records to check for
  /// inconsistent record lengths.
  first_field_count: Option<u64>,
@@ -536,7 +536,7 @@ struct WriterState {
 enum HeaderState {
  /// Indicates that we should attempt to write a header.
  Write,
- /// Indicates that writing a header was attempt, and a header was written.
+ /// Indicates that writing a header was attempted, and a header was written.
  DidWrite,
  /// Indicates that writing a header was attempted, but no headers were
  /// written or the attempt failed.